Parts: 1 (45-minute)
Writer: Russell T Davies
Airdates: 31 March 2007
Production Code: n/a

Doctor: tenth
Companion: Martha

Creature Feature: Judoon, Plasmavores

Story: Medical student Martha Jones has a problem - her brother's 21st birthday party is coming up, and she seems to be the one who has to mediate when her mother finds out that her father plans to bring his young gold-digging girlfriend to the celebration. But such worldly problems fade away just a bit when Martha gets to work, only to have the entire hospital transported to the moon around lunchtime. With most of the patients — and staff — unable to cope with this alarming change in location, Martha again finds herself being the voice of reason, as she tries to reassure the patients and try to find a way back. Fortunately for Martha, one of her patients is a certain John Smith, who joins her in her attempt to figure out what's happened to the Royal Hope Hospital.

Things soon become more clear when a flock of spaceships land just outside the hospital, and several columns of aliens march toward the building. They are the Judoon - intergalactic policemen of a mercenary disposition, currently occupied with the task of scanning every patient in the hospital to verify their human status. Which, the Doctor surmises, means that they must be looking for a non-human trying to stay hidden... and that, he tells a disbelieving Martha, means that he is in trouble too. With the Judoon hot on their heels, it's up to the Doctor and Martha to find the true intergalactic criminal hiding in the hospital... before it drinks their blood.