College student Amanda is babysitting for Helen and Dr. Cordell, watching after their young son at their large estate in the woods. When she arrives, the child, Tara, is already asleep; Helen and Dr. Cordell leave, Amanda makes tea in the kitchen, and is watched by a man through the window. After hearing odd noises, she is startled by the doorbell ringing, and finds her boyfriend Chris at the door. The two lounge on the couch before she makes him leave after Helen calls the home to check in. As Chris walks outside, he is attacked by a man hiding outside who clobbers him on the head. Amanda continues to hear knocking noises and believes it is Chris playing a prank on her. She opens a window to reveal a silhouetted face staring back at her. Panicked, Amanda calls the restaurant where Helen is dining with her boyfriend Jim and their friend, Dr. Cordell. Helen is notified by the restaurant staff and goes to take the call, but the line goes dead after she picks up. Worried that her ex-husband, Brian, may have arrived at the home, Helen has Jim call the local psychiatric institute, who notify him that Brian escaped earlier in the night; Helen reveals in conversation that he had been institutionalized after he attempted to murder her; Dr. Cordell is his doctor..... Directed by Peter Collinson Produced by Harry Fine Michael Style Written by Tudor Gates Starring Ian Bannen Susan George Honor Blackman John Gregson Music by Harry Robinson Cinematography Ian Wilson Edited by Raymond Poulton