The year is 1984, and a group of humanoids are running down a London alley. As they attempt to escape, they are gunned down by two policemen led by Commander Lytton. Two of the humanoids, Galloway and Quartermaster Sergeant Stein, escape to a warehouse where a time corridor is situated. Galloway is killed, leaving Stein alone.
Lytton transports back to his battle cruiser and prepares to attack a prison space station whose only prisoner is Davros, the creator of the Daleks.
Meanwhile, the Doctor, Tegan and Turlough are being dragged down a time corridor in the TARDIS (following on from the events at the end of Frontios). When the time machine lands, they find themselves in the London docklands in 1984.
In the meantime, the Daleks try a direct frontal assault on the prison station which yields poor results (and several Dalek casualties, as the station crew led by Dr. Styles, the CMO; and Lt. Mercer, fight back with considerable force). Lytton then persuades the Dalek Supreme to use poisonous gas to get the crew out of the way. The plan proves to be a success and the Daleks have little trouble taking over the ship. Following orders, Watch Officer Osborn attempts to kill Davros, first using an automated system that proves not to work, and then in person. However, Lytton and an engineer break into the cell and kill Osborn before she can complete her mission, instead releasing Davros from his cryogenic imprisonment (into which he was placed following the events of Destiny of the Daleks).
The Doctor and his friends have by now met a traumatised Stein, who joins them in returning to the warehouse to hunt for the end of the time corridor. There they meet a military bomb disposal squad, called in after builders uncovered what they thought to be unexploded bombs (and which the Doctor correctly predicts are in fact alien artifacts). While the others are distracted, Turlough stumbles into the time corridor, ending up on the Dalek ship.
Having learned that the Doctor is in the warehouse, the Supreme Dalek orders a Dalek to be dispatched to detain him. The Dalek travels through the time corridor and appears as if from nowhere. The Doctor yells at everyone to take cover as it prepares to exterminate them. (In the original four-part version of the story, this formed the cliffhanger ending of Part One.) The Dalek kills several of the squad's men before the Doctor advises them to focus their fire on its eyestalk, blinding it. In the resulting struggle, the humans push the Dalek out of the warehouse window and it explodes on hitting the ground; Tegan suffers a head injury and blacks out.
Meanwhile, on the prison station, only Styles, Mercer, and two guards are left alive of the original crew. Disguised in uniforms taken from Lytton's guards, they plan to blow up the station via its self-destruct system.
Speaking to Lytton, Davros explains that his cryogenic sentence lasted for "90 years of mind-numbing boredom." He then vows to take his revenge upon "that meddling Time Lord" — the Doctor. Lytton insists he is in their grasp. While Davros's travel chair is undergoing maintenance by the engineer (Kiston), Lytton explains that the Daleks lost their war against the Movellans due to the development of a virus that specifically attacks Dalek tissue, and have awoken Davros to find a cure. Despite Lytton's reservations, Davros demands that he remain on the prison ship while working on the virus, as it may be necessary for him to be refrozen. When Lytton leaves to discuss this with the Supreme Dalek, Davros uses a hypodermic-like mind control device to take control of Kiston.
Meanwhile, the Doctor and the members of the bomb disposal squad, having brought the remnants of the destroyed Dalek machine back inside, are searching for the Kaled mutant that was housed inside it. They eventually find and kill it but only after it wounds one of the squad's men. While the medical officer of the squad looks after the victim and a recovering Tegan, the Doctor and Stein head into the TARDIS to find out what is happening at the other end of the time corridor.
The TARDIS materialises inside the Dalek ship and, narrowly avoiding being captured by a guard, the Doctor tells Stein that they should find Turlough and make a swift exit. But Stein, suddenly no longer a stuttering coward, points his own weapon at the Doctor, revealing that he himself is an agent of the Daleks.
A squadron of Daleks close in to exterminate the Doctor, but Lytton, entering, informs them that the Supreme Dalek has ordered that the Doctor must not be killed - yet. The Daleks confirm this as the truth. The Daleks and Stien lead the Doctor away.
On the prison ship, Turlough joins forces with the remnants of the crew, informing them of the existence of the time corridor, as a possible way of escaping the effects of the ship's self-destruct.
On Earth, the man attacked by the Dalek creature is behaving very strangely and wanders away mumbling nonsense. The group commander, Colonel Archer, decides to radio for help, although his own radio is dead. He heads outside and finds two policemen (unbeknownst to him, Lytton's associates) and asks for assistance. As he tries the radio, a policeman holds a gun to his head...
The Daleks reveal their plan of cloning the Doctor and his companions, and to use the clones to assassinate the High Council of Time Lords on Gallifrey. Stien begins the mind-copying sequence while the Doctor tries to talk him into resisting his Dalek mind conditioning. While this is going on, Styles and the two station guards are killed when trying to activate the station's self-destruction system.
Back on Earth, Colonel Archer returns to the warehouse, obviously under Dalek control. Tegan makes an escape attempt, but is soon recaptured by the policemen and taken through the time corridor to the Dalek ship. The squad's scientific advisor, Professor Laird, is shot while trying to flee the soldiers.
Meanwhile, in the duplication chamber, Stein is overcome with confusion: the Doctor has realized that Stein's conditioning is unstable and begins challenging his ability to think for himself. Just as Stein's mind-copying sequence nears completion, he breaks his conditioning and stops the process, freeing the Doctor. The Doctor finds Turlough and Tegan, and they return to the TARDIS along with Stein and the last surviving station crew member. Rather than depart, the Doctor decides he must destroy Davros once and for all. With Stein and Lt. Mercer he heads to the station lab, leaving Tegan and Turlough in the TARDIS, which he has surreptitiously programmed on time delay to return them to the warehouse.
The Doctor confronts Davros in the lab, but his chance to kill him is lost when Stein's conditioning re-asserts itself long enough to let Lytton's troops kill Lt. Mercer. Horrified by his actions, Stein refuses to accompany the Doctor back to the time corridor, and runs off into the station.
Davros' army (now including a biochemist, Kiston, a soldier, and two Daleks) is growing and he dispatches his Daleks to Earth. Anticipating resistance from the Daleks not loyal to him, Davros breaks opens a capsule of the Movellan virus. Two Daleks then enter with the intention of exterminating him, but are themselves killed instead by the virus.
Back at the warehouse, a huge battle is taking place between Davros' Daleks and those loyal to the Supreme Dalek. The TARDIS has arrived and the Doctor (having returned through the time corridor) now knows that the alien artifacts discovered earlier on were in fact canisters containing the Movellan virus. He opens a canister that Tegan and Turlough have removed and brought into the TARDIS, and sneaks it behind the Daleks. Soon they all start to die.
Lytton has escaped, and gleefully watches the Daleks' demise. He swaps his Dalek uniform for that of a policeman, and joins his two fellow "bobbies" on their next vigil. Back on the station, Davros prepares to use an escape pod to flee from the station, but the Movellan virus attacks and seemingly kills him.
The Daleks are dead, and Tegan is appalled at the deaths that have taken place. The Dalek Supreme appears on the TARDIS scanner and threatens the Doctor, claiming that the Daleks have duplicates of prominent humans all over Earth, and it is just a matter of time before Earth falls.
Meanwhile, a wounded Stein is trying to activate the self-destruct sequence. Just as he is about to finish, the Daleks enter and exterminate him. With his last ounce of life, he leaps onto the console, completing the sequence and destroying both the station and the Dalek ship.
The Doctor calls for them all to leave, but Tegan says no — this has been one massacre too far. She no longer enjoys her adventures and wants to give it up, so she runs away. The Doctor is saddened by this, and he and Turlough leave. As the TARDIS vanishes, Tegan runs back, remembering the Doctor's old admonishment: "Brave heart, Tegan." She calls out to the empty air that she will miss him.
Doctor Peter Davison (Fifth Doctor)
Companions Janet Fielding (Tegan Jovanka)
Mark Strickson (Vislor Turlough)
Terry Molloy — Davros
Rodney Bewes — Stien
Rula Lenska — Styles
Maurice Colbourne — Lytton
Jim Findley — Mercer
Sneh Gupta — Osborn
William Sleigh — Galloway
Leslie Grantham — Kiston
Chloe Ashcroft — Professor Laird
Del Henney — Colonel Archer
Philip McGough — Sergeant Calder
Roger Davenport — Trooper
John Adam Baker, Linsey Turner — Crewmembers
Brian Miller, Royce Mills — Dalek Voices
John Scott Martin, Cy Town, Tony Starr, Toby Byrne — Daleks
Writer Eric Saward
Director Matthew Robinson
Script editor Eric Saward
Producer John Nathan-Turner
Executive producer(s) None
Production code 6P
Series Season 21
Length 2 episodes, approx. 46 minutes each
Originally broadcast February 8–February 15, 1984