Parts: 6
Writers: Robert Sloman, Barry Letts
Airdates: 4 May 1974 - 8 June 1974
Production Code: ZZZ

Doctor: third
Companion: Sarah

Creature Feature: Giant Spiders
Special Guests: UNIT (the Brigadier, Benton, Yates)

Story: Mike Yates persuades Sarah to investigate a local monastery where, he suspects, strange things are going on. He and Sarah conceal themselves in the cellar to observe a ritual, and to their shock, it results in a huge spider materializing in the center of the room. The spider jumps on the back of one of the monks, Lupton, who claims that they have become one mind.

Under the spider's guidance, Lupton steals the Doctor's blue crystal from Metebelis 3. They soon transport back to Metebelis, unaware that Sarah, hidden and spying, has also been transported. The Doctor follows in the TARDIS, and finds that Metebelis 3 is a changed planet. The human population is being dominated by the powerful spiders, controlled through fear and culled to provide the spiders with food.

When Lupton realizes that the blue crystal has been stolen back from him, he is forced to lie to the council of spiders in order to save his life. Now, to avoid death at their hands, he must recover it. The spiders want the powerful crystal at any cost - and nothing, not even the Doctor, will stand in their way...