The one where the Cybermen want to blow up Earth, the Doctor keeps shouting at Peri, and the TARDIS somehow learns to fix its chameleon circuit for five minutes.
Short Synopsis
The Sixth Doctor and Peri stumble into a convoluted Cyberman scheme involving Halley’s Comet, mercenaries, and a London sewer. The Cybermen want to prevent Mondas’ destruction, the Doctor wants to shout everyone into submission, and Peri just wants a new travel agent.
Extended Storyline
The adventure begins with the TARDIS doing the impossible: fixing its chameleon circuit. For about five minutes, it successfully disguises itself as a cupboard, a pipe organ, and a very unconvincing American-style police box before breaking again. This is played as a running gag, though honestly, the real joke is that anyone thought it would stick.
The Doctor and Peri land in 1980s London, where criminals are planning a diamond heist in a sewer. Of course, this isn’t just any sewer — it’s one with Cybermen squatting in it. Nothing says “classic sci-fi menace” like villains hiding in the same place as mutant turtles.
Meanwhile, on Telos (yes, the planet from Tomb of the Cybermen, because why write new lore when you can recycle?), the Cybermen have a master plan: hijack Halley’s Comet and smash it into Earth, thereby preventing the destruction of Mondas from The Tenth Planet. That’s right, the Cybermen have gone full Back to the Future, trying to rewrite history with an ice planet, a comet, and some good old-fashioned mass extinction.
But wait, it gets busier. The Cybermen are also using captured mercenaries and enslaved Cryons (icy alien women who look like they were sculpted from spare tinfoil) to guard their base. The Cryons are understandably annoyed about being kicked out of their home planet by a bunch of tin-plated stompy men and spend most of their time sighing about it in theatrical whispers.
The Doctor and Peri stumble between factions like pinballs in a particularly violent arcade machine. The mercenaries betray each other every five minutes, the Cybermen keep stomping dramatically into rooms to shout “EX-TER-MI—oh wait, wrong show,” and the Doctor spends most of his time either condescending to Peri or delivering continuity-heavy speeches to villains who don’t care.
Eventually, the Cryons convince the Doctor to help blow up the Cybermen’s base on Telos. The mercenaries mostly kill each other before the Cybermen can finish them off, and Peri spends a lot of time running around corridors looking exasperated.
The climax involves the Doctor sabotaging the Cybermen’s plan to redirect Halley’s Comet. Instead, the comet goes on its merry way through the solar system (thankfully not destroying Earth), and the Cybermen’s base explodes in a big pile of model work. The Doctor, having caused massive explosions and body counts, declares victory and sweeps Peri back into the TARDIS, presumably to yell at her some more.