In the distant future, the giant Starship UK
is equipped with a vast city. In a classroom, the children are called before the teacher, a two-faced mannequin known as a Smiler sitting in a booth. One face smiles and one frowns. They all receive good marks, except for Timmy. Afterward, Timmy talks to his fellow student, Mandy Tanner, who tells him he'll have to walk all the way to London, 20 decks away. She warns him that he'll be sent below. As she enters the elevator, a robed figure bars him from entering. Timmy takes the next elevator and another Smiler is waiting for him. A girl on a viewscreen starts reciting poetry and talks of going below, and the elevator descends all the way to floor zero. The floor opens beneath Timmy as he screams.
The Doctor has the TARDIS hovering in space, and holds Amy by her foot as he lets her dangle in the extended atmosphere a few feet beyond the doors. Once she has experienced space first-hand, he pulls her back inside. The Doctor then notices Starship UK
below, and explains that the human race evacuated Earth in the future when the surface was rendered barren by solar flares. Now Starship UK
is searching for a new home. Amy wants to go see it, but the Doctor reminds her that they are observers only, and he doesn't interfere. The Doctor turns on the scanner to the interior of the ship and Amy sees Mandy, crying. Amy sees the Doctor talking to the girl, and realizes that he's already landed the TARDIS, gone outside, and started investigating.
Amy runs out of the TARDIS and is amazed to find herself centuries in the future. The Doctor tells her to look around and figure out what's wrong. He grabs a glass of water from a couple and puts it on the floor, and then starts looking around again. He points out Mandy, sitting on a bench and crying silently. As they go to investigate, a robed figure, Peter, notices them and makes a call to his superior, Hawthorne. Hawthorne hears his report, says they're under orders to tell "her," and tells the man to continue watching the Doctor. Hawthorne then calls a robed woman and tells her that there's been a sighting. She asks if the Doctor did "the thing," and when she confirms that he did, says she'll watch him on the monitors. She then dons a porcelain mask and walks past a floor filled with water glasses.
The Doctor explains that Mandy is crying silently because she can't stop, and no one else is approaching her because they know what she's afraid of. He figures that whatever she's afraid of is everywhere, and they're in a police state. Mandy walks off but the Doctor knows where she's gone because she dropped her identity kit. He sends Amy to talk to Mandy, and points out that the Smiler booths are the only things that are clean and that no one approaches them. Meanwhile, he'll wander around and try to stay out of trouble.
Amy goes through the hallways and Mandy realizes she's being followed and confronts Amy. She realizes that the Doctor had her identification and walks off, but comes to a hole in the road. She tells Amy that they have to go around but Amy insists on pushing through the barrier and investigating. As Amy examines the locked cloth barrier, Mandy warns that no one is supposed to talk about Below. Amy ignores her and picks the lock, and Mandy explains that the Scots have their own ship. When she wonders if the Doctor is her boyfriend, Amy nervously says that she's almost definitely getting worried, and wonders what she did in what is now her past. Mandy notices that the Smiler is turning its frowning face around and says that Amy shouldn't go in, but Amy ignores her and crawls inside. She finds an electric torch and turns it on, revealing a wormlike extension that attacks her. Amy crawls back out and finds the robed men waiting for her. One gasses her unconscious with his ring.
The Doctor explores and finds a glass of water on the floor. The Masked Lady comes up and notes that the Doctor realizes the truth hidden inside of it, and that few people do. She knows him by name, tells him to keep his voice down, and asks what he knows. The Doctor explains that there's no engine vibration, and if there were, the water would move. He's discovered that none of the power conduits are connected, and there doesn't appear to be an engine. The Masked Lady asks for his help, saying he's their only hope. She gives him a tracking device to find Amy and says that she'll find him when the time comes.
Amy wakes up in a voting cubicle. There are three buttons, Protest, Record, and Forget. The computers identify her by name, but note that her marital status is unknown. A recorded message comes on and tells her that she is there because she wants to know the truth about Starship UK
, and she is entitled to know. Once the presentation is over, she will have a choice to protest or forget. If she chooses to protest and 1% of the ship's population do likewise, the programme will be discontinued with consequences for everyone. Otherwise they hope that she will choose to forget, which will cause her to forget what they have done to save everyone. The presentation then begins at lightning speed, and Amy immediately hits the Forget button. A message plays, a message that Amy herself has made saying to get the Doctor back to the TARDIS and stop him from investigating. The door opens and Amy finds the Doctor and Mandy outside. Amy stops the message and the Doctor asks what she's done.
The Doctor confirms that she's chosen to forget the last 20 minutes, and Mandy explains that everyone chooses to forget. She hasn't voted yet because no one is eligible to vote until they're 16. After that, everyone votes every five years. The Doctor confirms that the computer won't accept him as human, and admits that he's the last of the Time Lords. He then hits the protest button. The booth closes, sealing the Doctor and Amy inside, and the Smiler turns its frowning face. The floor opens and they both plummet down. Outside, the Masked Lady arrives and greets Mandy, who appears to know her.
The Doctor and Amy are shot through a high-speed air cannon and delivered 20 miles down into a rubbish dump. He realizes that they are standing on a tongue inside of a giant mouth. They discover that the mouth is closed, and the entire creature starts to shake. Vomit fills the chamber, flushing them out into another chamber. They end up in a pipe with only one door out, and a single button saying Forget. There are two Smilers nearby, and the Doctor goes to them and demands to know how things work. He refuses to forget and wonders what they're going to do. The Smilers emerge, but the Masked Lady arrives and shoots them down. She introduces herself as Liz 10 and brings Mandy in, and explains she tracked them using the device she gave the Doctor. When the Doctor asks if she voted, Liz 10 explains that she never voted and comes from outside. She explains that she and her family were brought up on stories of aliens of higher intelligence. As the mannequins star to self-repair, Liz 10 gets them out and talks about his exploits with Queen Elizabeth. The Doctor realizes she's the tenth generation descendent of the Queen.
Liz 10 takes them to a chamber filled with more of the wormlike tentacles, and the Doctor realizes that they're breaking through on multiple levels. The Doctor begins to realize what is going on, and tells Amy they should never have come. Amy remembers the message. As they move along, Hawthorne monitors them and initiates the protocol, noting "God save the Queen."
Liz 10 takes them to her chambers and explains that she keeps the glasses on the floor to remind her of the tyranny of the ship's government. When Amy comments on her age, Liz 10 explains that they've slowed her body clock and she's really 50. She tells the Doctor that secrets being kept from her, and the Doctor has achieved more than she has. Liz 10 has been working undercover, hence the mask. The Doctor points out that the mask is perfectly sculpted to her face. The robed men arrive and Peter says that Liz 10 is to be taken into custody. When she questions his authority, his face turns, revealing a frowning Smiler face on the back. Liz 10 insists that she's the queen and demands to know what on what authority she's to be taken into custody. Peter agrees that she is the highest authority and says that she must be taken to the Tower.
The robed Winders take Liz 10, the Doctor, Mandy, and Amy to the lowest part of the ship, the dungeon. More of the tentacles are caged nearby. Hawthorne is there and Liz 10 demands answers. He explains that citizens of low value are fed to the Beast, but it won't feed on children. The Doctor and Amy are the first non-children to be spared. The Doctor notices an electrical beam focused on giant cluster of skins, and explains to the others that Hawthorne and the others use pain prods on it to force the starship to go faster. The creature, a Star Whale, is Starship UK
. He frees one of the tentacles and uses his sonic screwdriver to let them hear the high-pitched constant scream of pain that it emits.
Liz 10 confronts Hawthorne and demands answers, and he says that he operates on instructions from the higher authority. She insists that she's the highest authority and orders him to release the creature, but they ignore her. The Doctor gives her the mask and explains that it's 200 years old but fits her perfectly. They slowed her body clock further than she thought, and she's 300 years old. She only remembers the last 10 years, and the Doctor tells her that she's relived the same 10 years over and over. He shows her a nearby panel with two buttons, Forget and Abdicate. Hawthorne explains that they work for her, and the Doctor plays a message Liz 10 made to herself where she explains that Star Whales lived in the depths of space. They captured the last of its kind and made it into Starship UK
when the citizens had no way to escape Earth. To continue on their way, Liz 10 must select the Forget button. If she selects Abdicate, the Star Whale will be released and Starship UK
will be destroyed.
After the message finishes, Amy wonders why she voted for this. Angry, the Doctor explains that she decided for him to spare him choosing between humanity and the Star Whale, and tells her that she was wrong to decide what he needed to know. He informs her that he'll be taking her home when he's done there and walks away. She challenges him, insisting it was one mistake, and tells her that she's only human. He then prepares to knock out the Star Whale's higher functions so that it will function as a starship without feeling the constant pain. The Doctor explains to Amy and Liz 10 that it's the only option, and angrily tells them that they have nothing more to say to him. Once he lobotomizes the Star Whale, he won't be the Doctor any more.
As the Doctor finishes his work, Timmy and the other children come in. Mandy is unable to get Timmy to respond. The Star Whale tentacle touches Mandy on the shoulder, and Amy remembers the Doctor's words to observe everything. Remembering everything she's seen, Amy tells the Doctor to stop and then takes Liz 10 to the Abdicate button and has her push it. The ship shakes and the Doctor asks what she's done. Hawthorne determines that they've increased speed, and Amy explains that the Star Whale volunteered. They tortured it only because they thought they had to. It couldn't let the children of Britain die.
Later, the Doctor looks out onto space as Amy comes to get him. She gives the Doctor Liz 10's mask and says she's promised there will be no more secrets. The Doctor notes that she could have killed everyone on the ship, but she points out he might have killed the Star Whale. He acknowledges that she stopped him, and Amy notes that all of the pain just made it kinder. When the Doctor warns that she didn't know how it will react, Amy says that she's seen another ancient being, the last of its kind, who took pity on children despite the pain it felt. They hug and go back to the TARDIS.
As they depart, Amy wonders about the Doctor taking her back to the next morning after they departed, and admits that she's wondered if he ever ran away from something he thought he wasn't ready for. He admits he did once, and that's why he is where he is now. As Amy starts to tell him the truth, she hears the phone ringing. Amy answers it and informs the Doctor that the Prime Minister is calling. When the Doctor asks which one, Amy confirms that it's Winston Churchill. The Doctor takes the phone and Churchill tells him that he has a very tricky situation. The Doctor assures him that he'll soon be there.. unaware that the shadow of a Dalek hovers over the Prime Minister.
The TARDIS departs, leaving the Star Whale to take the British people through space. No one knows that there is a glowing crack in the ship.