The Doctor (Troughton), Jamie (Frazer Hines) and Victoria (Deborah Watling) find themselves in London, being menaced by robotic yetis and the Great Intelligence again in this six-part story written by Mervyn Halsman and Henry Lincoln. The story ran from 3 February to 9 March, 1968, and saw the return of Travers (Jack Watling) from The Abominable Snowmen serial and the introduction of Colonel Lethbridge-Stewart (Nicholas Courtney), though apparently UNIT hasn’t been created yet.

The TARDIS is brought to a temporary stop in space as it is engulfed in a web-like fungus, which leads the Doctor and his Companions back to Earth, and the London Underground. It is here that a military group is fighting a losing battle against the spreading web fungus that is enveloping the subway routes.

This fungus is aided by the robotic yeti, which Travers unwittingly reactivated, despite what happened in Tibet, and has opened the doorway for the Great Intelligence to make another foray against the planet, and set up a trap for the Doctor.

As our heroes try to figure out a way to stop the Great Intelligence, a colonel shows up and takes charge of everything alongside the Doctor, Travers, and his daughter Anne (Tina Packer). He makes it quite clear though, that he is the final word on everything, well, him and the Doctor.

The Intelligence reveals its plan, it wants to sap the Doctor’s mind, adding the Time Lord’s intelligence to its own, a process that would leave the Doctor in a childlike state.

With the lives of his friends and all the soldiers hanging in the balance, the Doctor agrees to the process, but only after he’s developed some plans of his own…

He has reconfigured one of the yeti control spheres so now, the robotic creation is allied with our heroes, responding to commands that the Doctor, and then Jamie give it.

As the story races to our climax, the Intelligence seizes Travers, using him as a conduit, and kidnaps Victoria, holding her until the Doctor presents himself to have his smarts extracted.

When he does, he has a whole plan at work, he’s rigged things so that he can sap the Intelligence instead of the other way around, but during the final attack, Jamie and the gang remove the Doctor from the machine before he has a chance to execute his plan.

Everyone is delighted that they saved the day, but the Doctor is a little upset, instead of stopping the Intelligence once and for all, it escaped, and is still out there somewhere… waiting to return.

Also returning, though probably sooner than the Intelligence is Lethbridge-Stewart, who will appear in the story, The Invasion, this time as a full-fledged leader of UNIT.

But before that, the Doctor will have to suffer the Fury from the Deep! But he’ll have a little help, as yet another familiar Doctor Who trope will be added to the growing mythology…