Parts: 1 (45-minute)
Writer: Russell T Davies
Airdate: 14 June 2008
Production Code: n/a

Doctor: tenth
Companion: Donna

Story: The Doctor brings Donna to a leisure palace on the unlikely pleasure planet of Midnight, where the deadly xtonic radiation from the sun and a complete lack of atmosphere make it impossible to venture outside unprotected. Many people consider the planet worth visiting because of its unique composition: Midnight is made up largely of pure diamond, with glittering crystalline spires untouched by human hands, poisoned by the sun's lethal rays. The Doctor excitedly plans an outing to the famed sapphire waterfall, but Donna is uninterested in the eight-hour trip, far preferring to lounge by the pool and sunbathe under the protection of fifteen-foot-thick glass.

Setting off on his own, the Doctor soon makes friends with the entire complement of tourists aboard the shielded Crusader Tours truck: eminent scholar Professor Hobbes and his research assistant Dee Dee, the Cane family with their layabout son Jethro, and newly-single Sky Silvestry. But when a rockfall causes the truck to have to re-route through unexplored territory, a mysterious accident causes it to lose power, and strange banging noises come from outside. The passengers immediately fear the worst: that despite all evidence to the contrary, something is alive on the surface of Midnight... and it wants to get inside.