The BBC have released the official synopsis for episode one and two of Doctor Who series 6, The Impossible Astronaut and Day of the Moon.

Episode 1: The Impossible Astronaut

Four envelopes, numbered 2, 3 and 4, each containing a date, time and map reference, unsigned, but TARDIS blue. Who sent them? And who received the missing number one? This strange summons reunites the Doctor, Amy, Rory and River Song in the middle of the Utah desert and unveils a terrible secret the Doctor’s friends must never reveal to him.

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.

Episode 2: Day of the Moon

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 Impossible Astronaut airs April 23rd on BBC One/HD and BBC America.