Richard Blaney, a former RAF squadron leader, loses his job as a bartender at a Covent Garden pub and spends a bleak day lamenting his misfortune with his friend Bob Rusk, who runs a fruit and vegetable stall nearby. With no money to bet on the upcoming horse race, Blaney pins his hopes on a better break, while Brenda, his ex-wife who runs a successful matchmaking agency, hosts a tense visit that ends in a heated but brief argument before she invites him to dinner. The night ends with Blaney sleeping at a Salvation Army shelter, where a small, almost compassionate twist of fate occurs: Brenda has quietly slipped money into his coat.
The next day, Rusk arrives at Brenda’s office, a place now off-limits to her due to his unsettling reputation. In a moment of shocking violence, he rapes Brenda and then strangles her with his necktie, exposing himself as the serial killer the newspapers have dubbed the “Necktie Murderer.” When Blaney returns to Brenda’s office hoping for a chance to talk, he finds the building locked and Brenda gone. The discovery of Brenda’s murder immediately throws Blaney into the center of suspicion.
Seeking to prove his innocence, Blaney teams up with a former pub colleague, a plan that leads them to a hotel where they share a night of intimacy and a near escape from the pursuing police. They turn to one of Blaney’s old RAF friends for help, but the friend’s wife refuses to give shelter. Desperate, Blaney persuades his ally to retrieve his belongings from the pub, a move that backfires when the ally’s path crosses with Rusk, who rapes and murders her as well. The body is hidden away, first tucked in a sack and later loaded into a potato-laden lorry’s cargo area.
Back in his own room, Blaney learns that Rusk’s distinctive jewelled tie pin—an initialed symbol of the killer—has disappeared. Realizing the pin could incriminate him, Rusk races to recover it, but fate twists again as the lorry set in motion carries him along with the ticking clock of doubt. He exits at a roadside café with the pin still clutched in the dead woman’s hand, and returns to Covent Garden, where Babs Milligan’s body is eventually found. Blaney is then confronted with the far more damning implication that he might have a second murder on his hands.
Blaney, convinced that Rusk is the real culprit, turns to the man for help, only to be betrayed as Rusk offers to hide him while tipping off the police. The truth about Rusk’s guilt begins to crystallize, and the trial collapses into a dramatic contest of innocence and conspiracy. A chief inspector quietly questions the case, debating the right course of action with his wife over a dinner prepared with the questionable touches of an self-tashioned exotic cooking course.
From prison, Blaney vows to escape and seek vengeance. He engineers a jailbreak with the help of fellow inmates, who aid him in a dangerous pursuit to confront Rusk at his flat. Rusk is absent, but Blaney, certain that he is close, strikes a blow at the supposed target only to discover a lifeless woman lying in the bed, strangled by a necktie. Inspector Oxford, anticipating Blaney’s move, arrives as the situation intensifies. The pair are confronted by a fearsome sight—Rusk dragging a large trunk into the flat. With the sound of footsteps echoing in the stairwell, Rusk realizes that his game is up, and he drops the trunk in defeat as Blaney and the inspector close in.
