In the Third Doctor's last and most dangerous adventure, a misguided group of transcendental chanters forge an unnatural link with the evil spider rulers of Metebelis 3. Sarah Jane is invited by Mike Yates to visit him at a Buddhist meditation center where he has been staying. A group of people there, led by a man named Lupton, are misusing the meditation rituals in order to make contact with powerful alien forces, which manifest themselves as a giant spider. The spider is an emissary from the ruling council on the planet Metebelis 3, sent to recover the blue crystal that the Doctor previously found there, and that has now been returned to him by Jo Grant! Includes Tom Baker's uncredited first appearance.