Placing his life entirely in their hands, the Doctor agrees to search for the recipient of the fourth envelope - just who is Canton Everett Delaware the Third? And what is the relevance of their only other clue: 'Space 1969'? Their quest lands them - quite literally - in the Oval Office, where they are enlisted by President Nixon himself to assist enigmatic former-FBI agent Canton, in saving a terrified little girl from a mysterious spaceman.

The Doctor is locked in the perfect prison. Amy, Rory and River Song are being hunted down across America by the FBI. With the help of new friend and FBI-insider, Canton Everett Delaware the Third, our heroes are reunited to share their discoveries, if not their memories. For the world is occupied by an alien force who control humanity through post-hypnotic suggestion and no one can be trusted. Aided by President Nixon and Neil Armstrong's foot, the Doctor must mount a revolution to drive out the enemy and rescue the missing little girl. No-one knows why they took her. Or why they have kidnapped Amy Pond...

The TARDIS is marooned onboard a 17th-century pirate ship whose crew is being attacked by a mysterious and beautiful sea creature. Becalmed and beset by cabin fever, the pirates have numerous superstitious explanations for the Siren's appearance. The Doctor has other ideas but, as his theories are disproved and every plan of escape is thwarted, he must work to win the trust of the implacable Captain Avery and uncover the truth behind the pirates' supernatural fears – and he must work quickly, for some of his friends have already fallen under the Siren's spell...

The Doctor receives a distress signal from an old friend. Could there really be another living Time Lord out there? Hopes raised, he follows the signal to a junkyard planet sitting upon a mysterious asteroid in a Bubble universe, populated by a very strange family, as the time-travelling drama continues. The Doctor, Amy and Rory are given the warmest of welcomes by Auntie, Uncle and Nephew. But the beautiful and insane Idris greets them in a more unusual fashion – what is she trying to tell the Doctor? As the Doctor investigates, he unwittingly puts his friends in the gravest danger.

A solar tsunami sends the TARDIS hurtling towards a futuristic factory on Earth, where human doppelgangers are used to mine dangerous acid, as the time-travelling adventures continue. A second wave hits and the "Gangers" separate. They can remember every second of their "original's" life and feel every emotion they've ever experienced. But are these memories stolen or have they been bequeathed? Are the Gangers merely faulty machinery that must be shut down or are they living, breathing, sentient beings? Can the Doctor convince the terrified humans to accept these "almost people" and prevent an all-out civil war before the factory explodes?

As the solar storm rages, Jennifer, a Ganger driven mad by the memories of being "decommissioned", is seeking revenge, as the time-travelling drama continues. She can remember every excruciating second of every "execution" and is determined that the humans will pay. And she isn't just talking war; she's talking revolution. As the crumbling factory fills with toxic fumes and drips lethal acid, the "Originals" wait desperately for the shuttle from the Mainland to rescue them. But Jennifer has other ideas. Can the Doctor convince the terrified factory workers to embrace their own humanity and work together with their Gangers to overcome a monster of their own making?

In the desperate search for Melody Pond, the TARDIS crash lands in Thirties Berlin, as the time-travelling drama returns for the second half of the series shown earlier in the year. The Doctor comes face to face with the greatest war criminal in the Universe. And Hitler. Old friendships are tested to their limits as the Doctor suffers the ultimate betrayal and learns a harsh lesson in the cruelest warfare of all. As precious time ebbs away, the Doctor must teach his adversaries that time travel has responsibilities. And he must succeed before an almighty price is paid.

A little boy named George sends a distress signal to the Doctor when he discovers that monsters live in his bedroom cupboard.

The TARDIS brings its crew to a quarantine facility for victims of an alien plague. When Amy is trapped, Rory must rescue her from the facility's doctors but learns something surprising about his wife.

The trio arrive at a hotel where the layout of the rooms keeps changing. It also contains rooms that hold the greatest fears of each visitor.

As the Doctor prepares for his inevitable death at Lake Silencio, he visits a former roommate and learns that the Cybermen are responsible for a series of disappearances at a local department store and resolves to investigate.

As the Doctor makes his final journey to the shores of Lake Silencio in Utah, he knows only one thing can keep the universe safe – his own death – in the concluding episode of this series of the time-travelling drama. But has he reckoned without the love of a good woman?