Sasha Vredenburg, an untrained agent working for the Galactic Union, is assigned by Georgi Selestru to go to Astronomar. Her job is to report back to Selestru anything she can learn about the Dalek conquest. He tells her to lie low and stay out of trouble. She spends two years on Astronomar, fomenting rebellion against the Daleks, before being called back by Selestru.
She is surprised to be sent to Station Seven, orbiting Manikis. On a tour of the station given by Karlton, she is shown Dalek technology and Dalek prisoners in a Dalek saucer. She is also shown the "patients" on the station — former humans who are now Daleks. Selestru believes that one of the "patients" is Sasha's former mate, who was presumably captured by the Daleks.
Sasha is told that her job is to convince the Dalek "patients" to prevent the collapse of a nearby star, as the Daleks did with Astronomar's star. However, they refuse, because they only want to die. Sasha then tries to make a deal with the "pure" Daleks, who negotiate for the involvement of the "patients".
Unknown to the humans, the Daleks have tricked them. The "patients" restored power to the saucer, and the "pure" Daleks exterminate the "patients", giving them their wish. The Daleks tell Karlton how to stop the star collapse, which was caused by the "patients". Sasha, to save the station, sends the Dalek saucer, with herself in it, hurtling to Manikis' orbit, where it should burn up in the atmosphere.
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