London is in a panic. A sadistic serial killer is terrorizing the city, strangling women with the instrument which has earned him the moniker of the necktie killer. When the killer strikes Brenda Blaney (Barbara Leigh-Hunt), her ex-husband, Richard (Jon Finch) becomes the authorities’ prime suspect. He goes to his best friend, Bob Rusk (Barry Foster) with both grief over the death of his former spouse and concern over suspicions raised that he might be the killer since, as he assures his friend, he is completely innocent. But Richard doesn’t realize that he has turned to the wrong man for comfort and guidance. It is Bob Rusk who, in actuality, is the necktie killer and who now has even more opportunity to point police in the direction of his friend. Killing Richard’s girlfriend, Babs Milligan (Anna Massey), does the trick. Richard is arrested and police, despite Richard’s protestations of innocence, are certain they’ve gotten their man. But how many more women will die before they discover the truth?