London is held in the grip of a serial killer whose modus operandi is to murder his victims by strangling them with a necktie. When short-tempered ex-Royal Air Force officer Richard Blaney (Jon Finch) discovers his ex-wife (Barbara Leigh-Hunt) murdered, Blaney becomes a suspect. Forced to go on the run, Blaney attempts to take refuge with his best friend, fruit merchant Bob Rusk (Barry Foster), however Rusk may, in fact, be the necktie murderer himself.