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.