In 17th century England, a squad of soldiers led by Captain Simmons storm into the art studio of their employer's daughter, Matilda, and demand to know where the Doctor is. The artist feigns ignorance, but Simmons finds the Doctor naked, hiding beneath Matilda's dress. The Doctor insists it isn’t as bad as it looks.
In 2011, Amy and Rory return home from shopping and read up on how the Doctor was incarcerated in the Tower of London. She finds more entries.
During World War II, the Doctor engineers an escape from a German prison.
Amy figures that the Doctor is trying to get their attention, and notes that the Doctor said he’d get in touch two months ago. They get a TARDIS-blue envelope with a date and time, as well as latitude and longitude.
River Song is in a prison cell and receives a similar invitation. Shortly thereafter, the guards call in to report that the prisoner is packing to go to America.
Amy and Rory arrive in a deserted highway near San Juan School District, in Utah, in the United States, and find the Doctor waiting them for wearing a Stetson. As they exchange greetings, River arrives and shoots the Stetson off with a six-shooter. They go to a diner and River and the Doctor sync their diaries, and then the Doctor says that he’s done running, and he wants them all to go with him to somewhere new: Space, 1969
First they stop at a lake for a picnic. As they talk, Amy notices an alien figure silhouetted against the skyline. She starts to point it out to the others, but then forgets it. The Doctor points out the Moon and Rory notes that the first moon landing was in 1969. A truck pulls up and an old man waves to the Doctor. They turn and discover that a person in an American astronaut suit has appeared in the lake. The Doctor tells the others not to interfere and goes to greet the astronaut. He says he knows who it is, but the person opens their helmet. Amy and the others watch as the Doctor talks with the astronaut, and then the astronaut blasts him with energy. Rory and River hold Amy back as the Doctor drops to the ground, radiating gold energy. He says he’s sorry and starts to regenerate, and the astronaut blasts him again before walking back into the lake. River confirms that the Doctor is dead and shoots at the astronaut without effect.
As River explains that the astronaut shot the Doctor in the middle of his regeneration cycle, the old man walks up, carrying a gas can. He says that the Doctor said that they would need the gas, and River realizes they need to destroy the Doctor’s body to keep his enemies from obtaining it. She says that they need to do what they’re told, and Rory notices a nearby boat. They put the Doctor’s body into it and set it on fire, and then push it into the lake. River asks the old man who he is and why he’s there, and he says he came there for the same reason that they did. He knows them all by name and explains that he’s Canton Everett Delaware III. Canton tells them that he won’t be seeing them again, but they’ll be seeing him, smiles, gives them his envelope from the Doctor, and walks away.
The trio goes back to the diner and River points out that the envelopes are numbered two through four. River wonders where the first envelope is, but Amy says that it doesn’t matter. As River reassures her that the Doctor had a plan, Rory notices an opened TARDIS envelope on a table. They examine it and River figures that the Doctor sent the first envelope to the person he trusted the most. The Doctor emerges from the restroom and they quickly realize that he’s an earlier version of the Doctor who died, 194 years younger. River lies and says that they were all recruited to come to Utah and meet with Canton Delaware III. When the Doctor asks who recruited them, River says it was someone who trusts the Doctor more than anyone else in the universe. However, she refuses to tell him because of spoilers.
Back in the TARDIS, the Doctor tries to track down Canton and wonders why everyone is cross with him. Meanwhile, River explains in private that they encountered a future version of the Doctor, and they wonder what that future version had in mind. Amy wants to tell the current Doctor what they know, but River says that they can’t. She tells Amy that there’s a far worse day coming for her than her death or the Doctor’s. The Doctor determines that Canton in in Washington, DC on April 8, 1969, but says that he’s sending them all home because he’s going to ignore the mysterious summons. He asks his companions who sent the messages but they refuse to tell him. River says that he has to trust them, and the Doctor asks who she is and who she killed. When River refuses to answer, Amy asks the Doctor to trust her, insisting that he has to do it, and he wonders if she’s being threatened. When she denies it, the Doctor asks her to swear on something that matters, and she swears on fish fingers and custard. He accepts her word and puts his life in her hands.
A younger Canton is drinking in a bar when two agents come to get him. They explain that his boss wants to see him, and Canton says that he doesn’t have a boss. The lead agent tells him that the President of the United States wants to see him.
The Doctor checks the historical records and confirms that Canton was a FBI agent who got kicked out in 1969. Six weeks later, the President contacted him for a private meeting.
President Nixon tells Canton by phone that he needs someone on the outside with FBI training, and that Canton was his second choice. In the Oval Office, Nixon explains that every night for the last two weeks, he has received a call from neither a man nor a woman.
The Doctor puts the TARDIS on invisible mode and lands the vessel, and informs the others that the scanner doesn’t work when they’re cloaked. He starts to go outside, telling his companions to stay behind given the stakes. The Doctor emerges and finds himself in the Oval Office as Nixon plays a tape of the phone call for Canton. A little boy says that he’s scared of the spaceman and gives his name as Jefferson Adams Hamilton before hanging up. Canton suggests that the FBI investigate, but Nixon explains that the calls come to him no matter where he is and he wonders if the FBI is involved. They finally notice the Doctor, who tries to back away and stumbles into the invisible TARDIS. Canton tackles him and Secret Service agents arrive. River gets the scanner working and they watch as the agents start to usher Nixon out. The Doctor realizes River can hear him and tells her to make the TARDIS visible, and she does.
The Doctor takes advantage of the distraction to get to the President’s desk and says that he’ll take the case. River and the others come out and Nixon demands to know who they are. The Doctor claims that he’s an undercover operative Scotland Yard and says that the caller is definitely a girl, which means there’s only one place she can be calling from. Canton, bemused by the entire thing, asks where, and the Doctor asks for five minutes to explain. The former FBI suggests to Nixon that they give him five minutes and the President agrees. The Doctor takes command and concludes that the caller is in Florida because the caller mentioned spacemen, and NASA is in Florida. As the Doctor goes over street maps, Amy notices the same alien figure that she saw near San Juan. No one else seems to notice, but Amy remembers seeing the same figure from earlier. Rory interrupts her and Amy forgets again, but starts to feel nauseous. She asks to use the restroom, and the agents escort her on Canton’s okay.
In the restroom, Amy comes face-to-face with the same alien again and remembers the previous two sightings. The alien says nothing and a woman, Joy, emerges from the stall. She can see the alien and assumes that it’s wearing a mask, but when she turns away from it she forgets she saw it. When Amy points out the alien, the woman sees it again and make the same assumption, but then realizes she just said the same thing. The alien wipes her immediate memory again and lights flicker as the alien draws on the power and electrocutes Joy, blasting her apart. Amy uses her cell phone to take a picture of alien and asks why it killed Joy, and it says the woman’s name. It knows Amy’s name as well and tells her to tell the Doctor what he must know and what he must never know. The alien advances on Amy, who runs out into the hallway. Her escort, Phil, asks if everything is okay and notices her anachronistic cell phone. Amy says she has to tell the Doctor, but then forgets why she said it.
In the Oval Office, Nixon’s phone rings as the Doctor locates the one place the phone must be coming from. Canton advises Nixon to answer the phone, which he does, and the little girl says that the spaceman is here and is going to eat her. The Doctor and his companions enter the TARDIS and Canton follows them in. As they depart, Nixon assures the girl that he’s sending his best people.
In the TARDIS, Canton stares in shock at the enormous interior, while the Doctor explains that “Jefferson Hamilton Adams” are the names of three U.S. Presidents. When Nixon asked where she was, the little girl said the names, and there’s only one place all three names would appear. They arrive in Florida five miles from NASA, at a warehouse at the corner of Hamilton, Jefferson, and Adams Streets: the only place in America with those three streets at the same juncture. As Rory and Canton emerge, the Doctor points out that the phone was dead and it’s almost certainly a trap. They explore the warehouse, unaware that the astronaut is watching them from the shadows.
The group locates an alien box surrounded by boxes containing cutting-edge American space technology. The Doctor goes searching for the little girl, while Amy suggests they stop the spaceman in 1969 to stop it from killing the Doctor in 2011. River warns that they can’t alter their personal history. They find a power conduit running into a manhole and call over the Doctor. River goes down to explore the tunnels beneath the warehouse and finds more of the aliens, which move to confront her.
As Canton wonders if he’s still in a bar drinking, River emerges from the tunnels and says that they’re all clear. However, she asks for five minutes to explore some more, and the Doctor sends Rory with her. As they start exploring, River says that she feels nauseous. River determines that the tunnels are really old and wonders how no one noticed them. They find a locked maintenance hatch and River can’t resist opening it. As she works, Rory asks about the worse day coming for her that she mentioned to Amy. River explains that the Doctor met her as a young girl and knew everything about her, but they’re traveling in opposite directions. One day she’ll meet the Doctor and he won’t know who she is... and she thinks it will kill her.
The door opens and they find a large chamber with a strange console-like object in the center. An alarm goes off and Rory checks behind them. The aliens are advancing on him, and they make him forget he saw them. River examines the console while confirming that the tunnels run below the surface of the entire planet and are centuries’ old. The aliens approach Rory, drawing on the electricity, and River looks up in shock.
Amy asks Canton why he was kicked out of the FBI, and he explains that he wanted to get married, and it wasn’t allowed. He asks about the Doctor, and Amy explains that they’re friends, and then tries to remember what the alien told her earlier. They hear the girl cry out for help and go to investigate, and Amy feels the same nausea as earlier. She starts to tell the Doctor what she remembers, saying it’s important, but the Doctor goes off after Canton. They find him unconscious on the ground, and Amy finally tells him that she’s pregnant.
Before the Doctor can respond, the figure in the spacesuit walks into the room. It points a hand at the Doctor and opens its helmet visor, revealing a little girl inside. Amy grabs Canton’s gun and shoots the girl before the Doctor can stop her.