Doctor Who (Jon Pertwee) seeks to stop a group of well-meaning, but foolish, transcendentalists. Naively, the chanters foster an ESP link with the Metebelis Spiders, who don't exactly agree with the spiritualist's "all is good" philosophy. The spiders head to earth to recover a perfect blue crystal, and enslave some more humans while they're at it. It's up to the Doctor to intervene and -- once again -- save the entire universe. This was Pertwee's final episode.