Holistic Review: The setting and premise have enormous potential, but they're mired in an underdeveloped and confusing plot, leaving mainly the dialogue to keep the episode afloat.

Oh, I wanted to like this one so much.

I mean, it's the return of Rona Munro! Who is not only one of classic Who's few female writers, famously the writer of the classic series' final story, and the first classic-series writer to contribute a script to the revival, but also someone who knows how to write an interesting, multi-layered plot with meaningful themes. And yet, as much as I absolutely hate to say it, The Eaters of Light doesn't really show off those talents. Had this episode been written by, shall we say, a writer of whose work I'm less inclined to be forgiving, I would not think to myself "well, it's fine, because I know they can do better", and so I want to play fair with Munro too. But honestly, it's like criticizing a friend's favorite hobby... no fun for them and certainly no fun for me!

So let's get the worst out of the way. In my mind, there are two main areas in which the script lets the story down: the monster, and the dénouement.

The Eaters of Light have so much potential: I tend to find interdimensional aliens to be intriguing, and their design is so good (sure, they're the second crocodilian alien in a row, but those banded glowing tentacles!). However, those are the only two unreservedly positive things that I can say about them. In nearly every other respect, they're completely inconsistent, largely because what we're told is completely different from what we're shown. (The fault, therefore, may lie partly with the direction, editing and/or effects, for failing to make sure the visuals matched the script.) The episode left me scratching my head over these questions:

• On what do the Eaters of Light feed?
  This one should be self-evident, given their name: they feed on light. Their home dimension isn't pitch-black as we might expect, but apparently whatever illumination we're seeing is not the kind of light they can eat (either that, or they're just gluttons), because the Doctor claims that their motivation is to hunt down other dimensions of light where they can feed: "Once they break through, they eat. They will eat the sun, and then they will eat the stars, and they will keep eating until there are no stars left." This is a chillingly terrifying prospect, so the threat to the Earth should feel massive. The implication is that the monster that came through the gate is already feeding on the Earth's sunlight: "Every hour of sunlight that feeds it makes the world darker and the beast stronger." Soooo how come we never see any evidence of this? We never see it absorbing sunlight, nor does it even absorb the light from the fires that it runs past on its way to the cairn. It's not even clear how it plans to eat the sun and stars, since it doesn't seem to have the ability to fly except in its home dimension. In a story called The Eaters of Light, we don't get one second of it eating light or dimming the sky. Instead, we only ever see it feed on people.

• When do the Eaters of Light hunt?
  Again, this should be self-evident: one would assume that they hunt (sunlight) in the daytime. But maybe part of the reason we never see it absorbing sunlight is that we never see it in the daytime at all; we only ever see it hunting (people) at night. It does stalk and kill one Pict in the daytime (off-screen), so we know that it's not entirely nocturnal, but why is it nocturnal at all? Shouldn't it hibernate at night and come out to feed when the sun rises?

• How do the Eaters of Light kill people?
  Okay, fine, so the Eater of Light is totally ignoring the sun and munching on people instead. How is it killing them? From the two instances we see, it looks like the monster is sort of leaching the sunlight out of their bodies, leaving behind a monochrome husk. I don't understand how this could be possible, biologically speaking, since human bodies don't store up sunlight like batteries, but I can sort of accept it as a cool-if-inexplicable way to die, if for no other reason than that it would justify their name. Besides, interdimensional aliens don't necessarily have to adhere to the physical laws of our universe. But it's not internally consistent with what we're told elsewhere. First, when the Doctor finds a Roman corpse, he theorizes that "it's as if his bones have disintegrated... complete and total absence of any kind of sunlight", which implies that the monster is somehow speeding up its victim's timestream, aging them to death and beyond in a matter of seconds while blocking off (or absorbing?) every bit of sunlight before it reaches them. Again, cool — although I'm not sure how rapidly aging its victims would increase its sunlight intake, unless this process involves localized temporal acceleration — but not supported by any other facts. Second, when Bill and Simon are attacked, Bill claims that the monster was covering him in black slime. (He's taken so quickly that it's unclear how she notices this; we certainly don't see it, with Simon or Cornelius.) This slime is apparently excreted by its tentacles, as shown when the monster later smacks Bill on the neck and leaves behind a slime-print on her skin which shortly thereafter causes her to faint, the implication being that the slime is what incapacitates, kills, and/or ages the monster's victims. But the Eaters of Light don't seem to operate like spiders or triffids, who are used to delayed gratitude; if they feed by drawing some kind of energy out of a living human body, what good does it do to paralyze or envenom a victim who might then escape and die out of reach?

• Is sunlight helpful or hurtful to the Eaters of Light?
  I mean, you would assume helpful, right? After all, the Doctor claims that the sunlight is healing it: remember that line "Every hour of sunlight that feeds it makes the world darker and the beast stronger"? And yet the only way to heal from the monster's slime is apparently to let sunlight fall on it, which burns the slime away. If sunlight heals the beast, shouldn't it make the slime stronger too?

• Do the Eaters of Light attack their victims quickly or slowly?
  The implication is that they're fast killers: Simon and Cornelius are dead within seconds, and Lucius claims that the beast "laid waste to an entire legion in less than an hour." Soooo why does the monster just whip Bill's neck, when it's clearly within range to attack her? And when they flee up the ladder into the Pict roundhouse, how does it not catch Bill or especially the centurion behind her? It's practically nipping at her heels as she climbs the ladder, and its tentacles can clearly reach to the top, so why does it dilly-dally until they escape? The scene of Bill trying to outrun it in the forest is full of tension, but when the monster repeatedly gives up rather than eating the main characters, the tension begins to feel forced.

• On a final note, the black slime isn't the only bit of lore that appears out of nowhere: the Doctor also informs us, just before it becomes relevant, that the Eater of Light "feeds on light, but it homes in on sound." Yeeeeeeessssss, that makes total sense. Because sunlight makes a lot of noise.

So, frustratingly, the Eaters of Light are enormously inconsistent, with new characteristics appearing out of nowhere and not meshing with one another. This monster really needed to go back to the drawing board to be reconceived as an immediate threat with a logical goal and method of attack. Although the more I think about it, I realize that I don't even know how to rewrite the monster without making it too powerful. If it drained the light of the sun fast enough for the viewer to detect a noticeable darkening of the sky, that would probably result in the utter destruction of the Earth. Or if it flew off-planet where nobody could stop it from eating the sun, well, that would pretty severely restrict what role a bunch of second-century Romans and Picts could play in defeating it. The only option I can think of is that maybe it could drink the sunlight just out of the Earth's atmosphere, causing localized darkness while the sun still shines in the sky (which would be a pretty cool effect), and perhaps it uses its tentacles in self-defense when people try to attack it. But then you get a nigh-indestructible monster just standing in a field defending itself while it eats, and that sounds pretty boring. I'm beginning to think that this story needed to be reconceived from the ground up.

And speaking of reconceiving the story, it's time now to look at the way Munro wraps it up. Because, gosh, does that ever need to be rewritten. (I'm really, really not enjoying picking this apart, you guys.)

So I'm just going to come right out and say it: the Doctor's plan is kind of lame. If they're trying to figure out how to lure the creature back into the cairn and force it through the gate, since when is "let's lure the creature back into the cairn and force it through the gate" considered a "plan"? That's the bare minimum of a plan! I mean, it's not even a solution; it's the problem! And what exactly did the Doctor have to put in place to make it happen? Getting the Picts to play some music, and equipping people with a few more of the gatekeeping tools he's been pooh-poohing all episode? But, I mean, okay, at least his "plan" is going to work.

Or, I mean, more or less. To be honest, their strategy could use a little fine-tuning. In order to banish the Eater of Light, they have to keep it in the cairn until dawn, then force it back through the gate when it opens. They do manage to accomplish all of this, but only by some miracle. Instead of cornering the Eater of Light in the cairn, the Picts and Romans stay clustered in front of the gate, attacking the Eater of Light as it stands in the doorway. What stops it from simply turning around and leaving again? Nothing, that's what. The Eater of Light only stays in that cairn because it wants to (maybe it wants to eat them, or maybe they've annoyed it to the point that it just wants revenge). Had this been a better-conceived plan, they would have drawn it deeper into the cairn while the others blocked off its escape route.

Amazingly, that's not even the worst part of the so-called plan. No, the worst part seems to be that it puts everyone's lives horribly at risk. This monster is so fearsome and deadly, having slaughtered an entire legion and anyone else who wandered across its path, that both the Picts and the Romans cower in fear at the thought of running into it. Yet now they've invited it to join them in an enclosed space, leaving them trapped with only pointy sticks and magnifying glasses to defend themselves with — surely far inferior armaments to whatever the Ninth Legion wielded, yet this group is able to fight the creature back without even the slightest casualty. How do these handheld weapons stop the monster from lashing out with its killer tentacles? Is the Eater of Light even trying? (Again, we're back to the point that sometimes it seems content to just sit and watch, when it could instead slaughter its prey within seconds.)

Maybe part of the problem is that we don't even know how the gatekeeper's tools supposedly work. Sure, they look like TV aerials and lollipops, but maybe they wield some magic power? Otherwise, it's hard to believe that if this creature is so deadly on Earth, a single Gatekeeper would have any chance of holding back a whole swarm of them from the interdimensional gate. We're told nothing at all about the war club, which seems to be little more than a cleaving weapon; the magnifying glass, on the other hand, reportedly has supernatural properties. We're never told what the prism is made of, much less how the Picts can obtain and refine enough to make a handful of additional weapons overnight, but Ban informs us that "it poisons the light as the beast eats it." Well, okay. I can imagine a scenario in which this would be plausible, but that scenario would involve us, you know, actually seeing the beast eating light. Since we never do, the resulting effect looks like they're merely refracting colored lights onto the monster. (Pretty!) How or to what degree this poisons it — is it dying? is this why it doesn't attack anyone? — we're never told.

But okay, they've lured the Eater of Light into the cairn and forced it back through the gate. Here's where the trouble really starts. (What, you thought we were done? Alas no.)

As little sense as the monster makes, and as little sense as the Doctor's plan to banish it makes, Kar's plan to keep it banished makes the least sense of all. This is frustrating because I feel sure it made sense to Rona Munro, but we're given the explanation in dribs and drabs, and I don't think we ever get the whole picture. At least, it really feels like some key details are omitted. In this respect, at least, I think that poor Munro has fallen victim to the 45-minute curse.

Here's the thing: for untold centuries, the Picts have been surviving just fine by sending in one person per generation to fight the Eaters of Light. Now, suddenly, we're informed that that's not good enough, and will surely result in the Earth and the rest of the solar system being doomed. Why? Who knows. There are so many confusions in this whole process that it's difficult to even pinpoint what part doesn't make sense.

For starters, it's not clear exactly how the Picts have been protecting the gate up until now. Logically — since the gate only opens up once a year, for a few days when the sun's at the right angle in the sky, and for only a few minutes at dawn — it would make the most sense for the Picts to nominate one warrior to step into the gate for a couple of seconds on just those few days, to drive the Eaters of Light back until the sun passes and the gate closes again. There's apparently no worry about them getting trapped, since the Doctor is able to step back out after a couple of days when the gate is already closed. (That scene does, however, raise the question of why the gatekeeper is even necessary; when the gate opens, the Eaters of Light are just hanging out in the distance, paying it no mind. It's not like they're sitting around waiting to pounce the moment it opens for two seconds; had the Doctor not been there, none of them would have escaped.) During the rest of the year, there's no threat from the Eaters of Light at all.

However, the episode raises several alternative scenarios, and it's not clear which one is actually the way things work. Kar makes it sound as if one person per generation is chosen to defend the gate for that entire period, which the Doctor seems to corroborate: "One Pict in there, fighting it off for a few minutes, that adds up to 60 or 70 years out here." So what, every generation a new Pict enters the gate, fights for a few minutes in the creatures' dimension, and then doesn't come out again until — when? 70 years later on our side, not having aged at all? (But that's longer than a generation!) Or until they get tapped out by a replacement Pict after 20 to 30 years? Or until they die? That's what Bill implies, that the Gatekeepers don't survive: "Or are you gonna line up Picts sacrificing themselves until the end of the world?" Is that what happens? After a few minutes of fighting, the Gatekeeper is killed just in time for another one to take their place? In which case, how do the Picts know, each year when the gate opens, whether the Gatekeeper on the other side is dead or not?

At any rate, none of these possible scenarios explains why the Doctor feels so passionately that Kar can't go into the gate. If one person has been holding the gate for all these years, why is it suddenly problematic? What do short human lifespans have to do with anything, unless the Doctor is worried that the Picts will all die out and nobody will be left to protect the gate?

The Doctor also argues against letting two people protect the gate together, much less five, and in this case I agree with him, although I suspect we're objecting to different things. I agree with the Doctor that the gatekeepers are throwing [some brief period of] their lives away, and I agree that it is not equivalent to send Kar through the gate in the Doctor's place, because his lifespan is exponentially longer than hers. The difference is, the Doctor seems to think that having Lucius along will be helpful for Kar (though ultimately a death sentence for them both), whereas I don't necessarily buy that. It won't increase the length of time that they're able to protect the gate: as far as I know, Romans were not notably longer-lived than Celts, so Kar and Lucius are likely to die at roughly the same time. Nor is there a clear tactical advantage: one person can hold the Eaters of Light off without help, whereas adding more gatekeepers might actually cause problems, for a couple of reasons that I'll mention momentarily. I can only come up with two possibilities for what they might have been thinking. The first option: they plan for all five gatekeepers to attack the Eaters of Light simultaneously (ie, more powerful offense), under the assumption that having one or more sparring partners will help them survive attacks from the Eaters of Light longer, and perhaps beat them back more decisively. But we already know that the Eaters of Light can only approach the gate one at a time, and surely five gatekeepers can't all gang up on it at once? Wouldn't they just get in each other's way? Alternatively, the second option: if one gatekeeper dies, another is right there to take his or her place (ie, longer-lasting defense). But I don't see how this is any different from what the Picts have already been doing, except that a replacement is immediately available inside the gate's threshold. Besides, the second option is contingent on the idea that being a gatekeeper is a death sentence, and I'm not sure I believe that either. We've never been told that the gatekeeper job is invariably fatal, and there's no persuasive evidence that Kar, with or without Lucius, won't survive until she's replaced by the next generation's gatekeeper. As we've established, the job of guarding the gate doesn't seem to be all that dangerous — although I imagine it gets more dangerous the longer they stay inside (though, again, staying inside for more than two seconds seems to be unnecessary), as more Eaters of Light notice their presence and come to attack. So I keep coming back to the point that more than one gatekeeper is overkill.

Finally, is it not problematic that they break the rules? Regarding the Eaters of Light, the Doctor says that "they can only come through one at a time", and he later clarifies that this apparently applies to our end of the gate as well. (This is a completely arbitrary rule, but whatever.) So we should expect something catastrophic to happen when five people cross over at once, if the gate is only built to let one being through at a time. Instead, the ground rumbles a bit and shakes a few rocks loose from the cairn — ultimately seeming to block the gate entrance, putting the lie to the Doctor's claim "Well, they're not trapped." — but that's it. The cairn doesn't even collapse, which very well might lead to the Earth's destruction if it exposed the gate, enabling the sunlight to open the gate on a daily basis rather than a few days a year. (For that matter, we're told that opening the gate once a year is a release valve that similarly prevents the Earth from being destroyed; but if the gate is now covered up so that sunlight never reaches it, why hasn't it exploded yet?)

The rather glurge-y ending also leads to a lingering question: how are the gatekeepers all still alive in the present day? If 20 seconds in the gate is equivalent to 2 days outside, well, that's easy enough: 10 seconds per day. (Okay, okay, technically it's 2 days, 8 hours, 5 minutes and change, but let's round down and make it easier.) So if Lucius is 18 when he goes into the gate... oh yeah, never mind, that totally works. Assuming he has a lifespan of roughly 82 more years (ie, 2,585,952,000 seconds), that means he could live inside the gate for another 7,084,800 years in our time, if my math is correct. In fact, if Lucius went into the gate in 122 AD, by 2017 not even 3 months would have passed (by my count, about 80 days). Gosh. (Still, that is a long time to survive without food or water, while putting up a constant fight against deadly aliens. But maybe you don't need food or water in the Upside-Down.)

I mean, I should hate this story, right? This list encompasses a lot of problems. And yet, as frustrating and nonsensical as it can be, there's something about The Eaters of Light that makes it impossible for me to dislike. I grant you that some of this may be residual Munro-worship — Survival will buy you an awful lot of good will — but the story also has a couple of real bright spots. Neither of them is an unqualified success, mind you, but both lift the episode above the elements that bog it down.

First: I was put in an immediately good mood by the setting. Ancient Romans aren't particularly rare in Doctor Who, but Scotland is, and the Picts are making their first-ever appearance in the TV show. Add in some gorgeous location filming, which really helps bring the historical setting to life, and I could bask in that alone for hours. I also love that The Eaters of Light aims to offer a possible solution to a historical mystery; better yet, one I'd never heard of before. I love when Doctor Who becomes educational, and of course now I'm interested to read up on the history of the Ninth Legion.

Second: Munro knows how to write dialogue, and aside from a couple of borderline examples (I'm looking at you, Nardole), the script is excellent. A handful of scenes stand out in particular, and all of them involve Bill.

Now, Bill's start in the episode is a bit rough, as she overconfidently assures the Doctor, "You don't know more about the ninth legion than me!" Seriously, you're going to try to claim that you're more knowledgeable than the Doctor about anything other than human nature? Because you read a book? I believe the word "hubris" will apply here. But once we get past that scene, Bill goes from strength to strength.

For starters, Bill's chat with the Roman soldiers instantly humanizes Lucius and Vitus, while simultaneously pointing out how culturally self-centered we are. Bill thinks she's going to be too far advanced for their limited second-century minds, when in fact they think she's the one who's behind the times. Technically, this speech belongs to Lucius — who flips our expectations on its head when he reveals that in Roman times, liking only one gender is typically considered narrow-minded — but Bill's floored reaction is priceless. I don't know if all of Rome was really bisexual to the extent Lucius implies, but it's such a clever way to make us consider sexuality from a different perspective.

Bill: "Ahh. Lucius, erm, right, yeah, l- listen, there's, erm, something I should explain."
Lucius: "What?"
Bill: "This is probably just a really difficult idea. I don't like men that way."
Lucius: "What, not ever?"
Bill: "Nah. Not ever. Only women."
Lucius: "Oh, all right, yeah, I got it. You're like Vitus then."
Bill: (thrown) "What?"
Lucius: "He only likes men."
Vitus: "Some men. Better-looking men than you, Lucius."
Lucius: "I don't think it's narrow-minded, I think it's fine. You know what you like."
Bill: "And... you like... both?"
Lucius: "I'm just ordinary, you know, like men and women."
Bill: (laughs) "Well, isn't this all very... modern."
Lucius: "Hey, not everyone has to be modern. I think it's really sweet that you're so... restricted."

Next up, the scene in which Bill motivates the centurions to gather up their bravery and venture out of the caves. I have to imagine that this kind of scene is very hard to write, because how are you going to motivate a bunch of scared kids to risk their lives in a way that doesn't sound corny or trite? And yet Munro does it:

Lucius: "There is a beast of darkness that laid waste to an entire legion in less than an hour. No one man can make a difference to that!"
Bill: "Maybe that's what you don't learn when you think it takes five thousand highly trained soldiers to slaughter a bunch of Scottish farmers. Yes, one man can, and he's here."
Cornelius: "If you're calling us cowards, carry on. We already ran away, we know."
Bill: "You're not cowards. You're scared. Scared is fine, scared is human! I'll tell you what it isn't: it isn't a plan."
They consider her words.
Bill: "Right, listen to me, all of you. I'm going up there to find my friend. And if you come with me, I can't promise that you won't all die. But I can promise you this: you won't all die in a hole in the ground."

There's just something about this speech that's hard-hitting. Partly, I think, it's that although Bill is sympathetic toward her new friends, she isn't afraid to take them to task over their use of excessive force against the locals. But most of all, her line "I'll tell you what it isn't: it isn't a plan" is superb, because of all the comebacks I was anticipating, that was most definitely not one of them. And it's persuasive.

Finally, Bill boldly takes charge to de-escalate the fight brewing between the Picts and the Romans, physically interposing herself until they cool off. This is an especially proud moment for her character because Bill has apparently worked out that the TARDIS' telepathic field extends to the natives too, and seizes the opportunity to turn this knowledge to her advantage. I'm not particularly sure I buy that the Picts and the Romans think each other talks "like children", but since they are adolescents, it fits, and I admit it's a clever spin on the clichéd "I can understand your language, so now all our problems are magically solved" plotline.

I also really appreciated Bill's passion for history, even if some of her guesswork is off, as well as her excitement at visiting the past. As she wanders through the forest, and when she first happens upon Kar, her demeanour is that of a leisure tourist, excitedly exploring an exotic new locale. It's not until Kar gives chase that Bill suddenly realizes that her fun historical adventure is a bit more fraught with danger than she'd expected. Loved the expression on Mackie's face as she tells Simon's friends that he's dead, along with her delivery of "There's nothing here.", "Well, tell me!", and "No, we were both wrong about that."

Nardole falls between his two stools here: sometimes no-nonsense house mother, sometimes goofy sidekick. In terms of plot utility, he does basically nothing of consequence, but Lucas hits a number of lines out of the park, like the way he shakes his head no when the Doctor asks if Bill can see any marching legions, and his delivery of "Crows in the future are all in a huff?", "I'm rooted.", "You're back! They said you would probably never come back!", "Don't make me go squeaky-voiced.", and "No you most certainly are not!" But some of his lines made me cringe a bit, like his clichéd "I like what you've done with the place!", his return to explaining jokes as on "Welcome to our land. Heh, Scotch." and the anachronistic "I mean, I do a mean spag bol..." As you'll no doubt have guessed, I'm not ordinarily a big fan of characters making jokes that the other characters could never hope to understand, because they're clearly aimed at the viewing audience instead of the listener(s) in the story. (But I still laughed at the Doctor's line "What did you do, throw your action figures at them?")

Speaking of which: gosh, the Doctor sure is harsh in this story, isn't he? Losing Bill and fearing for her safety clearly has a bad effect on his temperament, but even before he knows she's lost, he's in no mood to play nice with the Picts ("That was the sound of my patience shattering into a billion little pieces!"). After Bill's disappearance, he's even less indulgent, repeatedly snapping at Kar: "You don't know anything, do you? You just stand around making speeches and waving a TV aerial about.", followed by "You'll hold them back? What, with your lollipop and your kiddie face paint and your crazy novelty monster-killing tool?" and the very pointed "You know, every moment you waste wallowing about in that happy thought means more of the living are going to join them." But this isn't entirely a bad change; on the contrary, it's a refreshingly brisk counterpoint to his more jolly outing in last week's Empress of Mars. Nor is he wrong: as admirable as Kar's determination is, she stands no chance against the Eater of Light, nor is her self-destructive attitude helpful. And sure enough, his tough love motivates her, albeit not quite in the direction he was hoping.

But then I could say the same about Bill: she's harsh, but not wrong either, when the Doctor attempts to give up his life to guard the gate, and she's forced to remind him: "This isn't your job!" (Though it might not be the best time to rub it in; Bill doesn't seem very concerned that the Doctor just got coshed on the back of the head!) While I appreciate that the Doctor is willing to sacrifice himself, and it's entirely in keeping with his character to give up his life in the service of — well, possibly just one remote village, or possibly the entire universe — there's a difference between giving up one of his lives to help people versus giving up all of them, and disappearing from the universe to boot. As Bill rightly reminds him, there are more people relying on him than just this one village, and even if the Eaters of Light have the power to destroy the universe, it's by no means a certaintly that they will, so it might be wise to consider alternatives to permanent self-sacrifice. (Anyway, we don't buy for a second that he might actually go through with this plan.)

Along with being less longsuffering and more self-sacrificial, the Doctor shows good insight when he immediately picks up on Kar's choice of words and the implications they entail: "I've got to wonder, what kind of a gate is that, and what's on the other side?" For the second episode in a row, the Doctor brokers a peace between the locals (in this case, the Picts) and the invaders (the Romans). And of course he turns out to be right about the fate of the Ninth Legion, which is really just as well; it wouldn't do to have his tutee, a newly-minted time traveller, show him up on historical expertise. In a way, The Eaters of Light has a bit of a throwback Hartnell-era feel, with the Doctor occasionally slipping into educational mode, as when he fills Nardole in on some of the essentials of Pictish civilization. I heartily approve! Capaldi gets to have some fun reversing the roles with Matt Lucas, in which Nardole becomes the Doctor's straight man for lines like "Yes, well, that's why we're hurrying, because there's not much light at this time of day."

Aside from the regulars, though, character development is another of the story's rocky areas. On the whole, the guest actors get a pretty raw deal here. No character gets more than one defining feature, with the possible exceptions of Kar and Lucius. Of the Roman characters, all at least get some lines, but among the Picts, only Kar and (to a small degree) Ban are speaking roles, so the tribe comes across as a pretty faceless bunch.

The first Roman we meet is Simon (Rohan Nedd), who forms a nice bond with Bill in their brief pair of scenes together. This is largely due to Nedd's (and Mackie's) skills as an actor; he adds interesting nuances to his lines that help to flesh out their budding friendship. Nedd gives a great portrayal of Simon as a slightly shell-shocked and skittish centurion (gosh, say that five times fast) who's struggling to overcome his feelings of inadequacy and shame. (Ooh! add "shameful" to the phrase up above and try it again.) He's a great facial actor; watch his expression in the scene where Simon's guilt at abandoning the Ninth is replaced by a mixture of fear and determination when the monster tracks them down. The fact that Simon is a centurion of color again explains why the Romans are so quick to treat Bill like a human being, but it's more believable than in Empress of Mars because the Roman empire did include soldiers from north Africa.

Lucius (Brian Vernel) greatly benefits from his rather cute crush on Bill, their heartwarming "friends forever" rapport, and his matter-of-fact acceptance of her sexuality, all of which makes him seem like a kind, likeable guy. But he also seems like a good leader, able to inspire his men and command their loyalty. And of course he winds up bravely giving his life (as far as he knew, anyway) to save the planet, which is about the most admirable thing any character can do. I really enjoyed Vernel's engaging performance, which made him the episode's most memorable guest star.

Cornelius (Billy Matthews) mostly comes across as a jerk, not wanting to share their food with Bill, and stubbornly insisting on barging up the ladder to safety before they've established that the way is clear. Matthews does a great job making Cornelius unlikeable while still making it clear that he's just a scared kid deep down. Still, I can't help but think: if they had to kill one of the centurions, at least they killed one of the less-likeable ones. I'd have been very sad if either of our two other centurions with a personality, Cornelius or Vitus, had been drained by the monster. And speaking of Vitus (Sam Adewunmi), his personality is pretty much limited to "gay and picky", but hey, it's something, and Adewunmi's performance on his few lines is amusing. I appreciated his convincing look of utter terror when he thinks he hears the monster moving ahead of them in the tunnels.

Thracius (Ben Hunter) only gets a few lines, Marcus (Aaron Phagura) even fewer, and the camera often isn't even on them at the time, so I can't say that either character was able to make much of an impression.

While Bill is getting to know the Romans, the Doctor and Nardole fall in with the Picts, led — in the aftermath of the massacre that claimed the lives of the adults — by the Keeper of the Gate, Kar (Rebecca Benson). Her plight is sympathetic: left to guard the Gate, and fearing what the Romans would do to her village, Kar — probably against her better judgment — allowed one of the Eaters of Light to get through the gate, in the hopes that pitting it against the Roman army would lead to mutually assured destruction. But it didn't; instead, as the Doctor caustically reminds her, "to protect a mighty little hillside, you doomed your whole world." It's clear that Kar has already realized the depths of her mistake, but is trying to put on a brave confident face to inspire her people and hide the crippling self-doubt she suffers. Alas, Benson's performance is limited by the fact that Kar doesn't get to (or Benson simply doesn't) deliver lines in many modes other than "shouty" and "sulky", but Benson gives a great performance as she remembers the loss of her parents, and on the line "You sound like children too."

Even more than Kar, there's something about Ban (Daniel Kerr) that I find believably adolescent. Maybe it's that Kar has shouldered her new adult responsibilities with such world-weariness, or maybe it's that Ban seems convincingly intimidated by the Doctor and distraught at the loss of his sister, but whatever the reason, Kerr gives a convincing portrayal of an adolescent forced into taking on grown-up responsibilities. (Also, is it just me, or does this Pict seem to be wearing braces? On freeze-framing him multiple times, I think they've just made him up to look like he has bad teeth, but man, it sure looks like braces from a distance.)

There are also crows. Oh, crows. I just don't know how I feel about talking crows... the payoff at the end is sweet, but otherwise it feels like a gag in a kids' TV show. And while I like Nardole's line "You were wrong. The crows aren't sulking. The crows are remembering.", it also sounds a bit eye-rollingly melodramatic. Anyway, the crows' lines sometimes don't even make sense. A couple of the crows, notably the one in the teaser, appear to be trying to say the Doctor's name, but why? And is there any real need for the crows to announce "monster!" since, without the heads-up, the characters would surely have noticed it mere moments later?

And then we get a coda featuring Missy, and oh my goodness, it's light-years better than anything before it. Michelle Gomez is such a firecracker of an actor, and her chemistry with Capaldi is just through the roof, that I find myself craving an entire season with these two actors, exploring the arc of Missy's redemption. I'm utterly glued to my seat to see what happens, and am rapidly concluding that five minutes per episode is nowhere near enough time to spend in her company. Love Gomez' performance on "Should I have stayed below decks?", her miming 'pick your jaw up off the floor' to Bill, and "Let's not get carried away!" I reluctantly admit that, even though I don't understand why listening to some music would make Missy cry — when the Doctor said "but you've never learned to hear the music", I assumed he was speaking metaphorically — and though intellectually I realize I should find this scene to be hokey and manipulative, there's something in the way Gomez and Capaldi sell the moment that has me totally hooked. And then there's this scene, which is so perfectly written that I could've watched hours more:

Missy: "I don't even know why I'm crying. Why, why do I keep doing that, now?"
Doctor: "I don't know. Maybe you're trying to impress me."
Missy: "Yes. Probably some devious plan, that sounds about right."
Doctor: "Well, the alternative would be much worse."
Missy: "Really?"
Doctor: "The alternative is that this is for real, and it's time for us to become friends again."
Missy: (overcome) "Do you think so?"
She moves toward the Doctor, but he backs away, though after a moment, he does clasp her hands in his.
Doctor: "I don't know. That's the trouble with hope. It's hard to resist."

It's utterly heartbreaking, but in the best possible way. I don't know, y'all, I take this as further evidence that Missy is genuine in her desire to change, but I guess we'll find out next week whether I'm right or whether she's made a fool out of me. But I still maintain that new repentant Missy versus, ahem, old unrepentant Missy would be a fascinating character study.

Was Murray Gold perhaps inspired a bit by Dominic Glynn's score for Survival? Because that's the vibe I was getting at various points, and I can't think of any other reason why a story about Picts and Romans would feature a soundtrack incorporating the flavor of Spanish guitars. If he was, I love it, and I love him for slipping in the reference. I also enjoyed the score as the Doctor and Nardole stumble across their first Roman corpse, followed by the obliterated Ninth Legion. The Picts' song is nice too, although its appearance in the teaser is so loud that I thought it was incidental music, rather than the music from the stones that Judy was hearing.

As I mentioned above, I really like the design of the Eaters of Light, especially their excellent glowing mouth-tentacles. Their banded blue "hunting" state is my favorite, but it's also very cool that the tentacles turn golden as they drain the life from people — this is a great effect with Simon, but even better when the color drains from Cornelius' body — and fade to a lifeless dull grey if crushed. I must admit, even though the plot seems to call for a monster that prowls the daytime, Palmer is wise to keep it to brief glimpses in the shadows; not that it's a bad design (quite the contrary) but it stokes the audience's curiosity about what the full creature looks like. Other than the monster, there aren't a lot of effects to speak of in this story. Except for the gate and the monsters' home dimension, which is a nice enough effect; I'm a fan of swirly blue glowing mists. But the ending, as the Picts and Romans vanish into the gate, reminds me a bit of Sapphire & Steel, but not in a good way. (I'm actually surprised to discover that I can be reminded of Sapphire & Steel in a not-good way!) Something about the way they slowly and very deliberately march into the gate just strikes me as cheesy, but then I'm probably being swayed by the incomprehensibility of the plot at that point.

Charles Palmer's direction is lovely, especially the way he frames the gorgeous scenery throughout the location filming.

I'm very proud of myself for staying almost entirely spoiler-free this week. The only one that slipped through was an article about Doctor Who's connections to Scotland, which I happily clicked on until the opening sentence gave away the fact that this article was important now because Eaters of Light was also set in Scotland. Drat. But as spoilers go, that one's fine; I'd completely forgotten about it until the very start of the episode, about half a second before the "SCOTLAND, PRESENT DAY" title appears.

Minor points:

• Again, we have a teaser that is entirely peripheral to the main story. Its only function is to show us that the music is still audible in the present day, and therefore that Kar and Lucius are (presumably) still alive. The teaser itself doesn't particularly grab one's attention — without hindsight, it's impossible to understand the significance of any of it, so it's not scary or intriguing as much as confusing — so again, I think it could've been excised.

• At the start of the episode, when it looked like The Eaters of Light was going to center around a stone circle and malevolent crows, I thought maybe we were in for The Stones of Blood redux. Alas no. (Then Bill strikes out from the Doctor to go marching into the forest on a solo quest, while being pursued by a beast lurking in the bushes, and it started to look more like The Androids of Tara. Wait! The Eaters of Light have squid-like tentacles, and the Picts have colorfully painted skin! There's The Power of Kroll sorted... Can we fit in any more of the Key to Time stories? Anyone want to argue that the gate operates like a time dam, or that the Atrions and Zeons are an allegory for the Romans and Picts?

• As the TARDIS crew emerged at a distance, I found myself hoping that one of the disembodied voices might be Missy. Sadly no! My Missy-as-companion story was not to be.

• I mean, really, who knows more about Romans than the Doctor? This reason alone is surely enough to establish his credentials!

  Doctor: "Speaking as a former vestal virgin second class, I can assure you..."

• What is Nardole eating? Gingersnaps? Animal crackers?

• How does Bill lose Kar so easily? One minute Kar's nipping at her heels, the next Bill has far outpaced her and lost her in the forest.

• Poor Bill, two tumbles down holes in the ground in two episodes running! (At least this time, the camera angle doesn't make it look like she smacks her chin against a rock.)

• Oh man, I love the way this is written! Naturally it appeals to my linguistics side, but I hadn't realized that Bill didn't yet know about the TARDIS' telepathic field — leaving it awfully late, aren't we?! — and it's pretty cool that she's the first companion to work it out on her own. Not only is she not wigged out, unlike several of her predecessors, she's actually pretty pumped about it. Her observations below are also a great subtle fit with her character trait of asking the questions that the audience is thinking but that nobody else has ever asked. The very last line is a total home run. (Also, this is a great performance by both actors; love the way Nedd delivers his second "I understand you".)

  Bill: "Aww, I wish I'd studied Latin so you could understand me."
  Simon: "I understand you."
  Bill: "Sorry, what?"
  Simon: "I understand you."
  Bill: "But, you're... but you're speaking English."
  Simon: "What's English?"
  Bill: "Uh, what you're speaking in?"
  Simon: "You're speaking Latin."
  Bill: "I'm not."
  Simon: "That's Latin. You just said that in Latin."
  Bill: "Ahhhhh, it's the Doctor! Or, or the TARDIS, or, or both? Something... telepathic... link... auto-translate! That's why everyone in space speaks English!"
  Simon: "What on earth are you talking about?"
  Bill: "Oh my god, it even does lip-sync."

• Munro, from Aberdeen, can get away with this one! (also LOL)

  Nardole: "Death by Scotland."

• With Bill's erstwhile pursuer now replaced by a prowling animal in the forest, I began to wonder if The Eaters of Light was actually a werewolf story. This tentative (and incorrect) assumption was not helped by the scene in which Kar storms back into the Pictish roundhouse, breathless and angry, just after the monster has attacked Bill, declaring "I destroyed the Roman army!"

• The frustratingly-unexplained slime is not helped by the scene in which Bill has apparently been smeared with it, yet we see no evidence of it until mere seconds before she faints.

• Is this another anachronistic joke? As far as I can tell, Jiffy Pop is not a popular UK brand, but...?

  Nardole: "Would you like some popcorn? Won't take me a jiffy to make."

• I thought all the adults in Kar's village had been massacred by the Romans? So did the Doctor: "Where are the grown-ups?" he asks Kar. But he's apparently been staring at a couple of them for the last few hours: in the overhead shot just before the Doctor lunges at Ban, we can clearly see at least two older bearded men in the roundhouse. The one on the left is probably in his early thirties, but the one on the right looks to be mid-fifties. Or whatever age was physically equivalent to mid-fifties in the second century AD.

• One of the best lines of the night. I LOLed! Such a wonderful classic-series feel to it, and the payoff is hilarious:

  Doctor: "But for now, would you mind awfully all just jumping out of your skins and allowing Nardole and I to escape in the confusion?"

• Kar's cutting it awfully close, arriving at the gate seconds before it opens. But then she never goes inside the cairn at all, apparently content to leave the Doctor to it. Wasn't she planning on, you know, "keeping" the gate...?

• When the beast was released from the cairn, why didn't it target the Picts to devour, rather than the much-further-away Romans? (If sound attracts them, maybe it was the noise from the encampment that drew it? Or perhaps it just realized it would get more bang for its buck by targetting the large Roman camp before the smaller Pictish settlement.)

• "Why do they call you Granddad?" asks Bill, asking the question we were all not wondering. We've heard one person (Thracius) call Lucius "granddad", only once, just now, in a mumble half-under his breath, so that the second syllable wasn't even audible. Yet Bill acts like this has been happening constantly.

• What happened before Kar's ancestors built the cairn around the gate to restrict it opening? How come an Eater of Light never got through the gate before there were gatekeepers?

• Very impressed that Bill works this out all on her own.

  Bill: "It's you, isn't it?"
  Doctor: "Yes, it's me."
  Bill: "Something to do with the TARDIS, maybe... telepathic field?"

• I may not be happy with how this scene turns out, but I love the line! (And Mackie's performance!)

  Doctor: "I've got a better idea this time."
  Bill: "Which is the part you never tell me!"
  Doctor: "Don't I?"
  Bill: "Uh-uh!"
  Doctor: "I probably just get interrupted."
  Before he can say anything more, loud music begins to play.

• "This is worse than jazz!" complains Nardole, followed by a hilarious expression courtesy of Matt Lucas. Methinks someone has never been woken up by free jazz on the radio at 7:00 am.

• Love this line, and Capaldi's enthusiastic delivery:

  Doctor: "Hey, you can name a cow after me!"

• Why exactly is Bill so upset that the Doctor has allowed Missy into the TARDIS? She barely knows anything about Missy, surely, aside from their brief meeting in The Lie of the Land, by which point Missy was fairly helpful and only a tiny bit outwardly psychotic. So what's there to object to?

Thanks to the regulars (including Missy), a spectacular setting, some charming dialogue, and a great dollop of untapped potential, I'm still going to rank The Eaters of Light as one of this season's above-average stories. However, its problems are just too numerous and too critical for me to be able to overlook them. It's like a soufflé that's fallen after coming out of the oven; still tasty, but deeply and disappointingly flawed.