The TARDIS is caught in a Kontron Time Corridor. After trying to free it, the Doctor (Colin Baker) and Peri (Nicola Bryant) strap themselves in to wait for the likely disaster. But once the TARDIS has entered the corridor, it stabilises and lands on the planet Karfel, a familiar world to the Doctor. In fact, there is a picture of the Third Doctor on the wall.
The population is ruled by a rigid hierarchy led by the Borad (Robert Ashby), a sadistic and despotic ruler. He is never seen in person but appears on security monitors as a dignified old man. The police are all androids, and rebels are dispatched via the Timelash—exiled into Time and Space. Acting for the Borad is the Maylin (Neil Hallett), the most senior of five counselors. One of them, Mykros (Eric Deacon) is disillusioned. The populace is rebelling and their former allies, the Bandails, seem ready to invade after the grain supply treaty is broken.
Mykros follows Maylin Renis into the power chamber. Renis is transferring the Karfelon power supplies to the Borad’s personal system. Renis supports the rebellion and is punished with being aged to death, and Mykros goes to the Timelash. Before this can happen, however, Vena (Jeananne Crowley), who is the daughter of Renis and the lover of Mykros, steals an amulet of power from Tekker (Paul Darrow), the new Maylin, and accidentally falls into the Timelash herself.
The TARDIS gives the sycophantic Tekker a chance to retrieve the amulet. He greets the Doctor and Peri as honoured guests, but the Doctor is suspicious of the whole society. He refuses to enter the Timelash, but Peri has been taken to the caves of the giant saurian Morlox to ensure his cooperation. Peri is rescued by the rebels Katz (Tracey Louise Ward) and Sezon (Dicken Ashworth) who kill one of the creatures. But they are taken captive by guards.
The Doctor returns the TARDIS into the Timelash and travels to Scotland in 1885. He finds Vena there and the stolen amulet, and a young man named Herbert. They return to Karfel. Tekker seizes the amulet and rounds up the time-travellers with the rebels. Sezon and Katz are sentenced to the Timelash. They fight back, killing Councillor Brunner (Peter Robert Scott) and sealing the doors of the chamber. The Doctor climbs into the Timelash on a rope and takes two Kontron crystals from the wall of the Time Corridor. Herbert follows and helps.
Tekkar flees to the Borad and blames all the troubles on the last loyal Councillor, Kendron (David Ashron), who is executed. The Borad is now revealed as a hideous cross of human and Morlox. They watch on a screen as Peri is strapped down in a cave with the Morlox creatures. Nearby is a cannister of Mustakozene-80, which will transform Peri into an ugly mutation.
The Doctor arrives and confronts Tekker and the Borad, who turns out to be Megalen, a crazed scientist the Doctor knows from the past, guilty of unethical experiments on the Morlox. The Borad is the result of one of those experiments gone bad and wants to replicate it to create a partner. He also wants to start a war with the Bandails which will wipe out the Karfelons, so he can repopulate the world in his own image. Even Tekker rebels at this, but he is aged to death. The Doctor uses a Kontron crystal to deflect Megelen’s beam back to him, resulting in his death.
Herbert helps the Doctor rescue Peri. The Doctor materializes the TARDIS in the path of the oncoming Bandail missile, destroying the missile. He returns to find Megelen (or his clone) alive, threatening the Council Chamber, mad as a hatter. The Doctor throws him into the Timelash to Scotland, where he may be seen from time to time in Loch Ness. The Doctor and Peri take Herbert back. He says he wants to stay on Karfel, but the Doctor is sure he must return to 1885, as he is Herbert George Wells and has work to do.
The story is rife with references to the Time Machine, The War of the Worlds, The Invisible Man, and The Island of Doctor Moreau. Timelash was largely panned by Doctor Who critics. The script, the sets, the production, special effects, and acting—even the costumes—were criticized. The H.G. Wells in the story has the wrong look, the wrong accent, and unlike the real H.G. is interested in spiritualism. The story almost bumped off the Twin Dilemma as the worst Doctor Who story. Paul Darrow purposely exaggerated his performance, based on Olivier’s Richard III, to retaliate for Colin Baker’s over-the-top performance in the Blake’s Seven series, in which Paul Darrow played Avon. But he is a hoot. The Borad, in contrast, though hideous, speaks quietly, like a man with real power. The idea that Borad becomes the Loch Ness Monster (He would have to grow considerably largely, I think) contradicts the Doctor Who story Terror of the Zygons, which has another explanation entirely. Efforts were made to tone down the antagonistic nature of the Doctor’s and Peri’s relationship, but it didn’t help much.