In 1984, a group of humans in futuristic uniforms is running down Shad James Street, near the London Docks. They are gunned down by two policemen led by Commander Lytton (Maurice Colbourne). But these police are not ordinary either. They are cold-blooded and unfeeling. They are, in fact, Dalek Troopers—brainwashed humans working for the Daleks. Of the future humans, only Sergeant Stien (Rodney Bewes) escapes into a wharf-building where a Time Corridor is concealed. Lytton transports back to his battle cruiser in the future to attack a prison space station, in which the only prisoner is Davros, creator of the Daleks.
The Doctor, Tegan, and Turlough are dragged down a Time Corridor in the TARDIS. They emerge in the London Docks. The Daleks assault the prison station, but are fought off by the station crew, led by Doctor Styles (Rula Lenska) and Lieutenant Mercer (Jim Findley). Lytton persuades the Supreme Dalek to use poison gas and the Daleks take over the station. Lytton and an engineer break into the cell and kill Officer Osborne (Sneh Gupta) before she can kill Davros. The villain is released. The Doctor and his companions meet Quartermaster Sergeant Stien and they return to the warehouse to search for the Time Corridor, where they find a bomb-disposal squad. Turlough stumbles into the Time Corridor and finds himself on the Dalek ship.
Finding out that the Doctor is in the warehouse, the Supreme Dalek orders him captured. A Dalek tracks through time to do this and kills several men until the Doctor tells the squad to fire on its eyestalk. The blinded Dalek is pushed out the window and explodes below. Tegan suffers a head injury and blacks out. Only Styles, Mercer, and two guards are left alive from the original crew. Dressed in uniforms taken from Lytton’s guards, they plan to blow up the station with its own self-destruct system.
Davros tells Lytton that he has been in cryogenic storage for ninety years and looks forward to revenge on the Doctor. While his travel-chair is being maintained, Lytton tells him the Daleks lost their war against the Movellans because of a virus. They hope Davros can effect a cure. Davros insists on remaining aboard the ship in case he needs to be re-frozen. He uses a hypodermic to gain mind-control over the engineer working on his chair, Kiston (Leslie Grantham).
The Doctor and Stien take the TARDIS to the other end of the Time Corridor and materialize inside the ship. The Doctor hopes to secure Turlough and leave, but Stien reveals he is an agent of the Daleks. The Supreme Dalek wants the Doctor alive, to clone him and his companions and use them to assassinate the High Council of Time Lords on Gallifrey. Stien begins to copy the Doctor. Tegan attempts to escape but is captured and taken to the Dalek ship. Davros uses his mind-control device to take control of the Daleks. In the duplication chamber, the Doctor is resisting and makes the unstable Stien stop the process. The Doctor finds Turlough and Tegan and they return to the TARDIS. The Doctor decides to destroy Davros. He sends Tegan and Turlough to Earth in the pre-programmed TARDIS. With Stien and Mercer, he confronts Davros, but Stien’s conditioning returns and Lytton’s troops kill Mercer. Davros sends his Daleks to Earth, intending to control them if necessary with the Movellan virus. He kills two disloyal Daleks. At the warehouse, there is a pitched battle between the Daleks of Davros and the Daleks of the Supreme Dalek. The Doctor returns with the Movellan virus and starts killing Daleks with it.
Lytton has escaped. He dons police clothing and joins the squad. On the station, Davros prepares to escape on a pod but the virus appears to kill him. Stien dies activating the self-destruct and destroys both the station and the Dalek ship. Tegan refuses to re-join the TARDIS crew, saying she no longer enjoys her adventures, but as the TARDIS de-materializes, she tells the Doctor she will miss him.
Terry Molloy played Davros because Michael Wisher was unavailable. The story was filmed at Shad Thames and Butler’s Wharf. It was criticized for its darkness and complicated plot and sub-plots. Lytton is the rare bad guy who survives, but we suspect both Davros and the Supreme Dalek are still alive somehow. In the mind-analysis machine, the Doctor flashes back to just about every companion of every doctor, except that Leela was left out by mistake. The Doctor shoots a Dalek mutant with a gun, and nearly does the same to Davros. There is a great deal of gratuitous violence, especially for a Peter Davison story. Of the three kinds of casualties in a story like this—the ones who deserve it, the ones who sacrifice themselves, and the bystanders who just serve to show how bad the bad guys are, there are an awful lot of the last category.