Retired British army captain and detective Hugh "Bulldog" Drummond is visited on his farm by his old friend, Inspector Mac McIver, who asks for help in solving a series of crimes. Mac thinks that the gang, whose robberies are characterized by precision and discipline, may be led by a former military officer and convinces Hugh to head an undercover operation. Footprints found at various robbery scenes indicate the gang frequents a waterfront nightclub called The Last Word, run by underworld figure Arthur "Guns." Sometime later, Hugh's old friend, Algy Longworth, worries after Hugh apparently disappears, and members of their London men's club tell him that Hugh was exposed as a card cheat. Algy cannot believe this, even though club board member Colonel Webson says that Hugh confessed prior to leaving the country. Meanwhile, in a flat in Chelsea, Hugh meets his assignment partner, Sgt. Helen Smith. Although Hugh balks at working with an attractive woman, he soon comes to respect her. Hugh calls himself "Joe Crandall," a career criminal who has been operating in Italy for the past five years, while Helen poses as his wife, Lily Ross. The next day, Helen deliberately crashes her car into Arthur's and as he approaches, she drops her handbag, revealing a gun. When a policemen appears, she tosses the bag to Arthur and he secretly asks her to meet him at The Last Word. That night, she tells him "Lily's" story, knowing that Arthur had followed her after the accident and read a seemingly incriminating letter in her purse. Hugh then arrives, pretending to be jealous, and while Arthur and Helen are dancing, searches his office. Later, Arthur dismisses the concerns of his jealous girl friend Molly because he has sent men to "Joe" and "Lily's" flat and concludes that they are genuine. The next morning, Hugh leaves the flat, aware that Arthur is watching. When Arthur knocks on her door, Helen plays up to him until Hugh telephones, and, within earshot of Arthur, she pretends to be talking with Joe about a job. She then says she has to leave immediately to help Joe out and rushes away, aware that Arthur's men are following her. In front of a police station, Hugh pretends to shoot a policeman, then gets into Helen's car and speeds away. Meanwhile, Algy learns that Hugh has been spotted in London and asks Webson to postpone a decision to oust him from the club, saying that Hugh must be on a case. Webson, who is the secret leader of the gang, becomes suspicious and orders Arthur to bring "Joe" to the British Museum on the pretext of meeting "Number One." Looking through an observation window, Webson recognizes Hugh. That night, at The Last Word, Arthur has his thugs tie up Hugh and Helen and prepare to throw their cement-weighted bodies into the Thames. Molly stops Arthur by suggesting that she assume Helen's identity and trick the police by tipping them off about a phony job while the gang pulls off the real one. Pretending to be Helen, she calls Algy and asks him to meet her at the club after confirming her identity with Mac. Arthur sets the stage at the club by closing it down and filling it with members of the gang and their girl friends. He then has Hugh tied to a chair and seats him next to Molly. Algy arrives and plays his part, pretending not to know Hugh, not realizing that he is actually doing exactly as Arthur and Molly have planned. After Algy innocently calls Mac with information about the job that Molly has described to him, he dances with her. When Hugh catches his eye, Algy sees Hugh's handcuffs and finally realizes that he has been setup. The gang, now dressed in military uniforms, departs for the job, leaving one man behind to guard the tied-up Algy, Hugh and Helen. The gang goes to Metropolitan airport and executes their plan to steal £500,000 in gold bullion from a military plane diverted to a distant runway. After stealing the gold, the gang eludes the police by changing into civilian clothes and moving the loot into another truck. After the gang climbs into the back of the truck, Arthur locks the door from the outside and rigs the engine to send carbon monoxide from the exhaust into the vehicle. At the hideout, Helen's request for a cigarette distracts the guard and Hugh is able to knock him out. With Helen's help, and a lighter, Hugh burns his ropes off just as the guard is coming to. The guard grabs a knife and throws it at Algy, wounding him, but Algy shoots him dead with his hands still tied behind his back. Just then, Arthur drives the truck into the hideout and Hugh draws the guard's gun. In a shootout, Arthur is wounded a moment before the arrival of Webson, who explains to Hugh that he started the gang because he felt useless and bored in peacetime. The police are right behind Webson and arrest him and Arthur. They then open the door to the truck, saving the lives of the choking men, but placing them under arrest. With the case over, Hugh tells Algy that he might like police work and walks off with Helen.