Jim Bankley, an amoral, opportunistic Canadian ex-soldier living in London, visits his old army friend Buddy to ask for help in finding a job. Buddy, who works for Sicilian gambling racketeer Rico Francesi, introduces Jim to his boss. Although Rico expresses no interest in Jim, Rico’s darkly dangerous sister Bella insists on hiring the ruggedly handsome Canadian. Later, at the Francesi headquarters at 44 Soho Square, Rico, furious that boxer Bill Walker has failed to throw a match, thus causing the organization great losses, sends strong-arm man McLeod to intimidate the fighter into following orders. After Bill responds to the threat by throwing a punch, the hot-headed McLeod retaliates by bludgeoning him to death. When Rico fires McLeod for attracting unwanted police attention because of his reckless behavior, McLeod tries to extort money from Rico. Jim, a friend of Bill, his boxing trainer father Tom and sister Betty, visits Betty to pay his condolences, but upon learning that Jim is now working for Francesi, Tom orders him to get out. Later, Bella invites Jim to go for a ride and drives him to her home, where she wastes no time seducing him. Betty, questioned about Jim by Inspector Collis of Scotland Yard, defends her friend’s integrity. Collis then asks Betty to continue her friendship with Jim to try to find out if he knows where McLeod is hiding. When Rico, the owner of a winning race horse, enlists Jim’s expertise as an ex-engineer to feed the bookies false betting information, thus increasing the odds on Rico’s horse, Jim proposes tapping into the bookies’ phone lines. At a café one day, Betty encounters Jim and innocently questions him about his job, but their conversation is interrupted by Bella. When Betty reports the incident to Collis, he advises her to forget about Jim. On the day of the big race, Jim successfully taps into the phone lines, and when Rico’s horse wins ten to one, Rico throws a party to celebrate. That night, McLeod sneaks into Rico’s house, but when Rico calls out for help, McLeod flees to a nearby warehouse. After Rico, Bella, Buddy and Jim pursue him there, McLeod, trying to escape, climbs on a rope suspended from the ceiling. Bella then goads her brother to cutting the rope, sending McLeod plunging to his death. Repulsed, Jim vows to get out of the rackets and hurries to Bella's house to pack his suitcase. Declaring that no one will ever leave her, Bella slaps Jim, and as the two struggle, Rico enters. Managing to escape, Jim seeks refuge at the Walker home, where a sympathetic Betty offers to help him. When Tom points out that Betty could be charged as an accomplice to murder, however, Jim departs. At 44 Soho Square, Rico informs Bella that he has arranged for them to leave the country that night by boat. When Bella insists on settling with Jim first, Buddy, Rico and Bella drive to the Walker house, assuming that Jim has taken refuge there. When Jim phones the house, Bella answers and threatens to harm Betty unless he comes immediately. Concerned about Betty’s safety, Jim phones Collis and, after he explains the situation, the inspector agrees to let Jim through the police lines with the proviso that he turn himself in afterward. As soon as Jim arrives at the Walkers', Buddy reports that two carloads of police have pulled up outside. Phoning Collis, Bella informs him that Betty will die unless they are granted safe passage. With Betty and Jim as hostages, Bella, Rico and Buddy climb into the car and head for the coast. As Buddy drives, Jim warns his old friend that he is next in line for betrayal and warns that the Francesis have no intention of taking him along on their voyage. Upon reaching the countryside, Bella orders Buddy to drive into the woods, after which Rico leads Jim and Betty into the underbrush, intending to kill them. Peering into the car’s trunk Buddy sees provisions for only two and, realizing that Jim was right, orders Rico to stop. Jumping out of the car, Bella shoots Buddy. Startled by the gunshots, Rico drops his guard and Jim wrestles him to the ground. Bella fires at Jim and misses, shooting Rico instead. Grabbing the disabled Rico’s gun, Jim shoots and wounds Bella, who fires back, then climbs into her car. Gravely injured, Bella swerves off the side of the road and dies. Wounded by Bella, Jim collapses, and as Betty huddles over him, the police arrive. One month later, a now recovered Jim is brought to trial, and due to the Walkers’ intervention, is sentenced to only two years probation.