England, the near future. Mike Yates, formerly of UNIT, is disturbed by odd happenings at a monastic retreat. Using Sarah as a liaison, he is able to warn the Doctor and the Brigadier. But how is the Doctor's research into ESP and the blue Metebelius III crystal connected to Mike's warning?
Elenco: William Hartnell , Patrick Troughton , Jon Pertwee , Tom Baker , Peter Davison , Colin Baker , Sylvester McCoy .