Amy is trapped in a quarantine facility where time moves faster than in reality, while the Doctor is confined to the TARDIS. Can Rory save his wife in time?
Amy is trapped in a quarantine facility for victims of an alien plague which could kill the doctor in minutes if he were to catch it. So Rory is the only one who can go into the facility to save her but can he save her before she is killed by kindness?
Having arrived at their intended destination, the Doctor and Rory have to find Amy who finds herself in a treatment facility that treats a particular kind of plague - one to which the Doctor is particularly vulnerable and would kill him should he contract it. The Doctor stays behind in a quarantine facility while Rory sets off to find his wife. In his first encounter with Amy Rory learns that 36 years have past and the Doctor, who is staying in the protective confines of the TARDIS, admits the time lines may be a bit wobbly. He's certain that he can find the Amy from their own time but there is only one thing blocking them - the older Amy who doesn't want the last 36 years to never exist.
- The Doctor, Amy and Rory travel to the world of Apalapachia, the second best tourist spot in the whole universe. However, unbeknownst to them the world is under quarantine due to an outbreak of Chen-7 the "one day plague" which results in death 24 hours after infection.
The TARDIS arrives in Two Streams, a "kindness facility" where the dying, through the use of temporal manipulation, are allowed to live out their natural lives. The Doctor and Rory enter the "green anchor" section for the uninfected, where time move normally. Amy accidentally enters the "red waterfall" section for the infected, where time is sped up. While those in green anchor watch their loved ones in red waterfall are allowed to live out a normal life in various constructed environments.
The Doctor soon discovers that Amy is trapped in Red Waterfall, after only a few minutes for him a week has passed for her. Using the monitoring device which allows communication between Green Anchor and Red Waterfall he constructs a tracking device which should allow him to lock onto Amy and enter Red Waterfall. Chen-7, while highly fatal to two hearted races such as Gallifreyan's, is harmless to humans and the Doctor instructs Amy to seek a safe hiding place, warning her that the ministrations of Two Stream's robotic tenders would likely prove fatal to her. Amy finds herself chased by several of the "handbots" and eventually seeks shelter inside an industrial portion of Two Streams.
The TARDIS arrives in the Red Waterfall section and the Doctor, who must remain inside or risk infection, sends Rory out to find Amy. Rory is soon attacked by handbots but is saved by a sword wielding woman who destroys the robots. She reveals herself to be Amy, who has spent 36 years living alone in Two Streams. Taking Rory to her hiding place, she reveals that she now hates the Doctor for having failed to rescue her decades before.
The Doctor determines that there is a way to go back in time and rescue young Amy from earlier in her life. However, older Amy refuses to do so, since that would erase most of her life. Rory argues that they should rescue both Amys and uses the alien monitoring device to allow the two Amys to talk with each other, convincing older Amy to try and rescue them both.
The Doctor agrees to help and instructs Rory on how to sabotage Two Streams' time engines in order to make both Amy's appear at the same time. Rory and both Amy's race to get to the TARDIS but are attacked by handbots. As older Amy fights them, Rory and younger Amy make a run for it. However, younger Amy is knocked unconscious by a handbot and Rory carries her inside the TARDIS. Older Amy is heartbroken when she sees the tenderness which Rory shows to her younger self, but her survival instincts win out and she runs madly towards the TARDIS.
Before she can enter, however, the Doctor shuts the door of the TARDIS in her face. He explains to Rory that he lied about being able to save them both and that there can only ever be one Amy in the TARDIS. In order to save older Amy they will have to leave younger Amy behind. The Doctor gives Rory the choice of which one to save. As they talk through the TARDIS door Amy and Rory express their love for each other and Amy urges him to keep the door locked, because if he doesn't she will not be able to resist entering the TARDIS. As the TARDIS dematerializes, older Amy allows herself to be anesthetized by the handbots.