Joe Banks (Inspector)Ned Beatty (Sgt. Logan)Lenny von Dohlen (William Dalton)Gerard Ender (Officer Cooper)Louise Fletcher (Miss Taylor)Tom Sean Foley (Gregg Howard)Julia Deane (Receptionist)Stoney Jackson (Tony Davis)Mary Jefferson (Miss Sloan)Lee Lively (Dr. Segers)Catherine McGoohan (Gloria Byers)Richard Rhodes (Policeman)Deborah Shelton (Leanne Dunaway)Dan Smith (Office Worker)Edward I. Swanson (Rev. Swanson)Robert Vaughn (Mr. X)Charles W. Ambrose (Office Worker)Paul C. Baker (Office Worker)
William, a lonely mail-room employee, is obsessed with Leanne, a beautiful secretary in his office, who also just happens to live in the apartment opposite his. At home he spies on her with a telephoto-lens camera, and one night he sees her having sex with another co-worker from the office, Greg. Shortly afterwards Greg is murdered, and Leanne begins to suspect that William might have done it.