Timelash was the fifth story of season 22 of Doctor Who. It was notably the last story of the classic era to revolve around an adventure with an historical figure, H.G. Wells.
The Doctor and Peri are arguing over their next destination when the TARDIS is ensnared by a Kontron tunnel, a time corridor in space. After the Doctor fails to free the ship, he and Peri strap themselves in. The TARDIS approaches the corridor and is nearly torn apart by the impact, but stabilizes once it has entered the corridor. It is navigated to the source of the disturbance, the planet Karfel, a world the Doctor has visited before. Before they get there, the translucent image of a woman glides through the console room.
On Karfel the small population is ruled in a rigid hierarchy. At the apex is the Borad, a sadistic and despotic ruler. The Borad has never shown himself in person, only via security monitors which show a dignified old man, but something in his manner does not ring true. Fear is enforced rigidly through the policing of androids. Rebels such as Aram, Gazak and Tyheer are dealt with either by summary execution or dispatch and death via the Timelash – a permanent, and ultimately fatal, exile down a corridor of time and space. Below the Borad is the Maylin, in effect a proxy mayor figure, the most senior of the five Councilors of Karfel. These Councillors are more cyphers than people of true council. One of them, Mykros, has grown unhappy with the rule of the Borad. Since the Borad came to power, their people have become disillusioned, rebellious and miserable. Their former allies, the Bandrils, are poised to invade. The Bandrils threaten war after the Borad rescinds thegrain supply treaty, which underpinned the relationship between the two civilizations.
Mykros determines to discover the truth and follows the Maylin, Renis, into the Borad’s power chamber. The unhappy Maylin is transferring the power supplies of the Karfelons into the Borad’s personal system, despite the danger to his own wife, who is recovering from hospital surgery. Renis finds Mykros and gives him his blessing in rebellion. However, the Borad finds out and metes out the usual punishment: the Maylin is aged to death in a deadly beam while Mykros is sentenced to the Timelash. Before he can be sent in, however, Vena, Renis’ daughter and Mykros’ lover, intervenes to plead for his life. When this fails, she steals an amulet confering the power to pervert the energy supply from the new Maylin, the sycophantic Tekker, and accidentally falls into the web of the Timelash herself.
The arrival of the TARDIS presents Tekker with an opportunity to retrieve the amulet. The clever Maylin greets the Doctor and Peri as favored guests, but the Doctor is suspicious of a Karfelon society that has made huge scientific leaps in a short time and that does not permit mirrors. When the Doctor refuses to venture into the Timelash again, Tekker explains that Peri has been taken hostage to ensure his co-operation in retrieving the amulet. She has been taken to the caves of the Morlox, large lizards indigenous to Karfel, where her captors hope she will die. Yet luck is as ever on her side — as well as some Karfelon rebels, Katz and Sezon, who kill one of the creatures threatening her and take her into their company. However, they are soon attacked and captured by a patrol of guards.
To protect Peri, the Doctor returns the TARDIS into the Timelash. He calculates the normal path of the Timelash would send Vena to 1179 on Earth, but the interference of the TARDIS (which she passed through and the Doctor and Peri had seen earlier) caused her to end up in Scotland in 1885. When the Doctor arrives he finds Vena, the amulet and a justifiably agitated young man named Herbert. All three depart on their return journey to return the amulet – which is all Tekker cares about when the TARDIS arrives back in the Council Chamber.
The Doctor, Vena and Herbert are rounded up with the rebels Mykros, Sezon and Katz and condemned to the Timelash. They fight back, killing the toadying Councillor Brunner and sealing the chamber doors, determined to hold out in a siege. This buys the Doctor enough time to hoist into the Timelash on a rope and take two Kontron crystals from the wall of the time corridor. He uses this to create a time ruse, allowing him to slip out of the chamber. Herbert follows.
Tekker has fled to the Borad. He blames the setback on the last remaining loyal Councillor, Kendron, whom the Borad executes. Tekker remains at the side of the Borad, now revealed as a hideous amalgam of human and Morlox. Together they watch on a screen as Peri is brought into a cave and strapped down while Morlox gather to feed. A canister of the chemical Mustakozene-80 is placed nearby. This can fuse together different tissue as one creature. It seems the Borad has taken a liking to Peri and wishes to mutate her like himself. The Doctor arrives to confront Tekker and the Borad, recognizing the latter as Megelen, a crazed scientist he encountered on his previous visit to Karfel and exposed to the Counsel for unethical experiments on Morloxes. It seems one of those experiments has now gone wrong and Megelen wishes to replicate its effect to create a partner. His plan has been to provoke a war with the Bandrils with bendalypse warheads, which will wipe out all the Karfelons — but leave the Morlox and himself alive, allowing him to repopulate the world in his own image. This revelation prompts Tekker to rebel, but he is swiftly aged to death. The Doctor uses a Kontron crystal to deflect Megelen’s beam back at him, killing the mutant in his wheelchair.
Herbert helps the Doctor rescue Peri from the Morlox. They return to the Council Chamber where Mykros and Vena have identified a Bandril invasion fleet armed with bendalypse warheads. It is close to Karfel. The Bandrils are suspicious of the Doctor’s attempts to intervene and prevent a missile strike. He takes drastic action. He materializes the TARDIS in the path of the incoming warhead, risking his own life to save Karfel. He succeeds and returns to Karfel to find Megelen returned from the dead and threatening the Council Chamber — or, rather, the other one was a clone of this original. Megelen is unbalanced by the image of himself in a boarded up mirror, revealing the reason he hid himself away. He is thrown into the Timelash by the Doctor, who says the Borad was sent to Loch Ness.
In the TARDIS, the Doctor and Peri prepare to depart Karfel to return Herbert to his own time. Herbert is still outside and the Doctor calls to him to hurry up, before showing Peri Herbert’s calling card, which identifies the young man as “Herbert George Wells”.