Planet of the Spiders is the fifth and final serial of the 11th season of the British science fiction television series Doctor Who, which was first broadcast in six weekly parts on BBC1 from 4 May to 8 June 1974. It was Jon Pertwee's final regular appearance as the Third Doctor, the last regular appearance of Mike Yates, and marks the first, uncredited appearance of Tom Baker as the Fourth Doctor. This serial introduces the term "regenerate" to explain the Doctor's transformation into another appearance. The serial is set in England and on the planet Metebelis Three. In the serial, the fired salesman Lupton (John Dearth) allies with a race of psychic spiders called the Eight-Legs to gain power. Plot Following the events of Invasion of the Dinosaurs, Mike Yates was discharged from UNIT and is now attending a Tibetan meditation centre in rural England. Sarah Jane Smith visits him and they witness some curious events, seemingly organised by a resident called Lupton, and his cronies. Mike and Sarah stumble across Lupton performing an incantation, which conjures up a giant spider. It jumps on Lupton’s back and then disappears. The spider manifests itself in Lupton’s head, telling him to seek out and locate a certain blue crystal. The Third Doctor has developed an interest in psychic ability, but his testing of a clairvoyant called Professor Clegg backfires when his subject has a fatal heart attack. It is triggered when Clegg comes into contact with a blue crystal from Metebelis Three (sent back from the Amazon by Jo Grant), which caused him to see the image of deadly spiders. Sarah returns from the retreat, and she and the Doctor swap spider tales. Meanwhile, Lupton has also arrived at UNIT HQ and steals the crystal from the Doctor’s laboratory. A multi-vehicle chase ensues, which Lupton escapes by teleporting back to the monastery. There, the spider reveals that it is plotting against some of its sisters back on Metebelis Three. The spiders and the crystal originate from the same blue planet in the Acteon Galaxy the Doctor last visited during The Green Death. The Doctor and Sarah make for the monastery and tell the deputy abbot, Cho-je, that something is very amiss. The crystal is taken by Tommy, a handyman with learning difficulties, whose mind is opened by the crystal's power. Lupton is teleported to Metebelis Three, unwittingly allowing Sarah to follow him.