When Dr. Martin (Robert Powell) arrives at the Dunsmoor Asylum for the incurably insane, he expects to be interviewed by asylum director Dr. Starr. Instead he is met by Dr. Rutherford (Patrick Magee), who explains that Dr. Starr had suffered a mental breakdown and now is one of the patients. Dr. Rutherford decides that if Martin can deduce which one is really Dr. Starr, then he will be given the position. Is it Bonnie (Barbara Parkins), whose affair with a married man turns murderous? Is it Bruno (Barry Morse), a hardluck tailor visited by a mysterious stranger (Peter Cushing) with a blueprint and very special fabric for an unusual suit? Is it Barbara (Charlotte Rampling), accused of murdering her brother and her nurse but insisting that her friend Lucy (Britt Ekland) was responsible; Or is it Dr. Byron (Herbert Lom) who claims the ability to transfer collecting?