Rory and The Doctor Leaving the TARDIS

The Doctor takes his travelling companions Amy Pond and Rory to the planet Apalapucia, supposedly a top holiday destination. But they arrive in a clinically white room, its only exit is a door with two buttons that open it – a green one and a red one.

As they start to explore Amy steps back into the TARDIS to collect her phone. Rather than wait for her to return The Doctor and Rory pass through the door using the green button. Shortly afterwards Amy follows but by uses the red button. Both groups find a similar white waiting room with a glass scope in the centre of it, but for The Doctor and Rory there is no sign of Amy. While for Amy there is no sign of The Doctor or Rory.

When The Doctor realises that Amy has not joined them, he discovers that she has ended up in a second, faster time stream, but is able to communicate to her through the glass scope. He also discovers that despite them only being in the room for a few minutes a week has already passed for Amy. The Doctor and Rory are soon joined by a faceless, white robot, who explains they are in the Two Streams Facility, which is assisting in dealing with a plague known as Chen7 that affects only races with two hearts, including the native Apalapucians and Time Lords.

Rory and The Doctor

The robot, and others like it, do not recognise The Doctor and Rory as alien life forms, and so attempt to administer injections that would be fatal to them. The Doctor warns Amy of this, and tells her to wait, as he will rescue her. He and Rory then race back to the TARDIS with the glass scope, using it to lock onto Amy's time stream to effect her rescue.

Because of the Chen7 virus The Doctor is forced to stay in the TARDIS while Rory, with The Doctor’s sonic screwdriver and the glass scope, sets off to find Amy. The Doctor also gives Rory a set of glasses that allows him to see, hear, and communicate with Rory to help him locate Amy.

The Doctor Communicating with Amy

Rory explores more of the facility, but soon is set on by more of the robots. He is saved by a much older Amy, now a fugitive hiding from the complex's sensors. The Doctor realises that he locked onto the wrong time stream of Amy, and tries to get Rory to convince the older Amy to help locate the younger one.

But Rory finds that the older Amy has become bitter, having waited as The Doctor instructed, and otherwise has been alone for 36 years save for the complex's computer interface and a disarmed robot she has come to call Rory. At first the older Amy refuses to help, knowing that by saving the younger version of herself, she would cease to exist.

Eventually The Doctor detects signals from the younger Amy nearby, and Rory finds her through the glass scope, crying to herself. Rory sets the scope to allow the older Amy to speak to her younger self, but the older Amy reiterates that she experienced this before, and hearing her future self warn about the time streams convinced her to wait out for rescue.

Amy

Rory though manages to convince the younger Amy to change her mind. This though results in the older Amy to demand that The Doctor take her too, a difficult but not impossible task for the TARDIS. The Doctor agrees, and as Rory re-routes a control panel that maintains the facility's time streams, The Doctor helps the two Amys to synchronise their thoughts, letting the two exist at the same time.

With these changes, The Doctor's glasses fail, and Rory and the two Amys must race through groups of robots to make it back to the safety of the TARDIS. But as they near its location, the older Amy falls back to protect the other two. However, the younger Amy runs into a robot and is sedated. As the older Amy covers his back, Rory takes the younger Amy into the TARDIS, upon which The Doctor slams the door behind him, telling Rory that it is impossible for both Amys to exist in the same time stream. He then gives Rory a very difficult choice to make of which Amy he wants.

He and the older Amy have a tearful farewell at the TARDIS door before the older Amy tells Rory to move on without her. As she does so she is taken by the robots just as the TARDIS dematerialises.

Inside the TARDIS Amy wakes up and asks The Doctor and Rory where her other self is. Neither The Doctor nor Rory can answer her. The Doctor though decides that after what they have just experienced that it would be best to leave Amy and Rory alone together.