Zoe, now in her late fifties, is approached by a young woman, Ali, who's positive she's met her -- a much younger version of her -- before. She's aware that her memories have been tampered with, and accepts Ali's offer of help to try and reconstruct the events of their previous encounter. Fortunately Ali has the necessary equipment with her, so they can get started straight away...

Ali, it transpires, was working at the Whitaker Institute in Australia when the TARDIS showed up, with the Doctor, Jamie and the younger Zoe. Exploring the facility, they discovered computer records detailing patients with terminal diseases -- who, apparently, were nevertheless discharged. Then they ran into another intruder, who was looking into stories of strange goings-on, involving the word 'Achromatics'. When he set an alarm off, guards arrived and in the confusion Zoe got separated from the others. She found herself in a room with unknown alien lifeforms floating in vats: the Achromatics.

The Achromatics, it turned out, had unusual powers. But these weren't supposed to include roaming the Institute and killing people...

!!Tropes
* CallBack: [[spoiler:Ali's employers]] have listened to Zoe's counselling sessions from ''[[Recap/BigFinishDoctorWhoCCS1E2FearOfTheDaleks Fear of the Daleks]]''.
* ChekhovsGun: The cut on Zoe's hand.
* CommonalityConnection: Like Zoe, Ali was a lonely child prodigy working in an isolated base. [[spoiler:Subverted. Her backstory was faked to gain Zoe's trust.]]
* FriendlessBackground: Zoe lives alone, and has no friends or family, which she puts down to the damage to her memory.
* GroinAttack: Performed accidentally by Zoe on Jamie, when they're forced to hide in a wardrobe.
* ImpersonatingAnOfficer: In the time it takes for Zoe to be captured and interrogated, the Doctor has convinced everybody that he's an agent of the Company and Jamie and Zoe are his subordinates.
* MeaningfulName: The Achromatics are named for [[spoiler:[[Literature/ThePictureOfDorianGray Dorian Gray]]]].
* NoPlansNoPrototypeNoBackup: Enforced by the Doctor, Jamie and Zoe; they destroy all records of the Achromatics before their departure. [[spoiler:However, the Company have realised there's still a copy of the plans in Zoe's eidetic memory.]]
* SequelHook: At the end of the framing story, an offer is made to Zoe. [[spoiler:Her memory restored in exchange for her knowledge of the Achromatics. She rejects it, and wonders if the Company might come back with a better offer... or turn nasty.]]
* UnreliableNarrator: [[spoiler:Not Zoe, but Ali; she was never there, and the passages she narrates never took place.]]