Sarah wakes up to find the Doctor awake and planning their next move: riding in the android capsules to land ahead of Crayford's ship. But he's uncertain that they will survive the re-entry.
At the real Devesham, they are tracking Crayford's return. The real Harry and Benton wonder where the Doctor and Sarah are, having found the abandoned TARDIS in the woods. As Crayford descends, the pods launch and are mistaken for meteoroids. The Doctor emerges safely and starts looking for Sarah.
Sarah finds the TARDIS and seemingly the Doctor. But when he tries to let the Kraal invasion happen, she realizes it is an android and runs off. The android Doctor and the android Sarah set off for the Defence Station.
Crayford's ship lands and Colonel Faraday and Sullivan go aboard. The Doctor arrives and calls them back. But the takeover has already started: an android Benton is already in place. And the Doctor is able to discern that both Faraday and Sullivan have been replaced. He is able to escape with Sarah.
The Doctor heads to the scanner room, bluffing his way past the Benton android, to see if the technicians have finished a circuit he designed for them that will disrupt the androids. The android Doctor tries to stop him and shoots the technician. But Crayford arrives before he can kill the real Doctor.
The Doctor and the android tell Crayford about Styggron's real plan to wipe out humanity. Even Crayford's crash was faked: his ship was pulled off course and he was given an eyepatch over a functional eye to fool him into believing their story. Crayford rushes off to confront Styggron, allowing the Doctor to fight his android off and push the control, disabling every android in the station.
Sarah boards Crayford's ship, frees Harry and Faraday and is then confronted by Styggron, who is astonished that she has not died of the virus. Crayford confronts Styggron, who shoots him down. The Doctor then arrives and fights Styggron. He is shot but Styggron falls onto the virus container and is instantly killed. The Doctor collapses, but it turns out it was the android, reprogrammed by the Doctor.
The Doctor and Sarah return to the TARDIS. Sarah wants to take a taxi home, but the Doctor persuades her to come with him…