The Doctor and Liz are summoned to the Wenley Moor Research Centre by the Brigadier, after several staff members suffer nervous breakdowns.
Quest roles:
Nicholas Courtney(Brig. Lethbridge-Stewart), Norman Jones(Hieronymous), Fulton Mackay(Dr. Quinn), Ian Cunningham(Dr. Meredith), John Newman(Spencer), Cy Town(Haemovore (uncredited)), Peter Miles(Nyder), Thomasine Heiner(Miss Dawson), Roy Brannigan(Roberts), Bill Matthews(Prison Officer)