Doctor: Matt Smith (Eleventh Doctor)
Companion: Karen Gillan (Amy Pond)
Sophie Okonedo – Liz 10
Terrence Hardiman – Hawthorne
Hannah Sharp – Mandy
Alfie Field – Timmy
Christopher Good – Morgan
David Ajala – Peter
Catrin Richards – Poem Girl
Jonathan Battersby – Winder
Chris Porter – Voice of Smilers/Winder
Ian McNeice – Churchill
Directed by Andrew Gunn
Written by Steven Moffat
Script editor Brian Minchin
Produced by Peter Bennett
Executive producer(s) Steven Moffat
Incidental music composer Murray Gold
Production code 1.2
Series Series 5
Length 45 minutes
Originally broadcast 10 April 2010
In the distant future, deadly solar flares force humanity to evacuate Earth on giant, nationalistic colony ships. The Doctor and Amy arrive on Starship UK, one of the last ships to leave and holding the population of the United Kingdom. Amy tends to a crying young girl ignored by adults while the Doctor, curious to the ship's engines, seeks the control room. He finds the room to be a false front, and encounters Liz 10, who seems to know him.
Meanwhile, Amy calms the girl, named Mandy, and learns that her friend had disappeared in a hole on the ship. Despite Mandy's warnings about the robot-like Smilers and their monk-like Winders that maintain order on the ship, Amy investigates a tented area around the hole. A tentacle-like entity emerges, and she backs out into a group of Winders. They take her to one of many voting booths set up on the ship. She is shown a video about the truth of Starship UK, and then asked if she wants to "protest" the truth or "accept" it, the latter causing her short-term memory to be wiped. Amy chooses to accept, and creates a video to herself to prevent the Doctor from learning the truth, before the mind wipe. By then, Mandy had led the Doctor to the booth as Amy finishes watching the video to herself. The Doctor is curious as what "protest" will cause and activates it, sending he and Amy into the maw of a giant creature below the ship. The Doctor induces the creature to vomit, allowing them to escape back to the ship, where Liz 10 and Mandy helps them avoid the Smilers and Winders after them. As they flee, Liz 10 explains she is Queen Elizabeth X, the ruler of the ship.
The Winders eventually capture the group, and they are taken to the Tower of London. The Doctor discovers that Starship UK rides atop a giant Star Whale, and controlled by sending painful electrical impulses to its brain via a control panel in the Tower. Liz 10 recalls she was the one that ordered this, and had chosen to wipe her memory to forget that action, creating the voting booths for the rest of the population to do the same, as they fear if they "abdicate" and release the Whale from this slavery, it will destroy Starship UK. The Doctor is furious, not only at having to chose between saving humanity or the Whale, but also at Amy for trying to keep him from making that choice. The Doctor decides to make the Whale brain-dead, allowing it to continuing travelling. As the Doctor starts the process, Amy observes Mandy has found her friend, unharmed. She forces Liz 10 to hit the abdicate control; to everyone's surprise, the Whale continues travelling, at a faster speed. Amy posits that like the Doctor, the Whale had come to Earth willingly to help save the remaining children, and is helping Starship UK.
The Doctor and Amy reconcile and return to the TARDIS after saying their goodbyes. Amy is about to tell the Doctor of her impending wedding when she is interrupted by a call to the TARDIS from Winston Churchill, who is face-to-face with a Dalek.