Because nothing says “horror” quite like being trapped on the Circle Line with killer Yeti and no way to get a seat.
Short Synopsis
The Doctor, Jamie, and Victoria land smack in the middle of London’s Underground system, where robot Yeti are rampaging, the tunnels are clogged with creepy fungus, and the Great Intelligence is back to try yet another scheme involving mind control, goo, and bad real estate choices.
Extended Storyline
The TARDIS narrowly avoids being smothered in weird space cobwebs (which would make for a very different sort of pest-control episode) before landing in the London Underground. Unfortunately, “avoiding cobwebs” doesn’t last long, because the Great Intelligence has returned with a swarm of Yeti and enough fungus to turn the Tube into a walking hazard.
Meanwhile, London is under martial law, because apparently the combination of rampaging furballs and sticky tunnels proved too much even for British stiff-upper-lipness. Enter the military, led by Colonel Lethbridge-Stewart — making his very first appearance before earning his promotion to Brigadier. He and his troops bravely set up barricades in the tunnels, despite looking very much like they’re doomed extras in a war movie.
The Doctor and his companions bumble into this mess and quickly figure out that the Intelligence is using robot Yeti to spread its webby fungus throughout the Underground. The plan? Turn the entire city into one giant cobwebby brain-control hub. Because if you’re going to enslave humanity, why not start with the commuters who are already miserable and halfway broken?
Suspicion brews as no one’s quite sure who’s secretly under the Intelligence’s influence — leading to more paranoia than a locked-room mystery weekend. The Doctor cobbles together various bits of gadgetry to fight the Intelligence, while Jamie does most of the legwork (literally, running up and down tunnels) and Victoria screams just enough to keep the tradition alive.
Eventually, the Doctor prepares a plan to trap the Great Intelligence in his own device — essentially turning its attempt at mental possession back on itself. But before he can actually pull it off, one of the humans sabotages his machine out of “good intentions,” leaving the Intelligence to simply… float away into the ether. The Yeti stop working, London is freed, and the military lives to underfund another day.
The Doctor is, of course, cross that his “perfect” plan was ruined, but at least the Yeti didn’t end up running the Circle Line permanently — though arguably, that would have been an improvement over the usual service.