Gangster Nick Biaggi is telephoned from Paris by Aggie, his brothel madam. She says that she's found the perfect girl for him: Malou (Marie-Louise), a French waitress, whom she lures by means of framing her for a staged theft and offering her protection.
Cab driver Johnny shows off his new taxi to his colleagues, but one of Nick's henchmen deliberately rams it as his boss watches. Nick tells Johnny that he was a witness and offers him a drink. Spotting Johnny's Canadian regimental insignia, Nick claims that a Canadian saved his life during the war, and insists on sorting things out with the loan company (actually one of Nick's businesses).
Malou arrives at Aggie's Blake Street address. Aggie shows her a lavish wardrobe and offers her a dress to try on. Nick silently observes Malou from behind, and Aggie jokes that he resembles a customer.
Nick tells Johnny that he needs to find an eligible bachelor for an arranged marriage, and offers £200.
Malou meets Vicki, one of Aggie's more experienced girls, and asks her about her job, but is merely told that she's in the entertainment business. Vicki thinks Malou resembles her sister Maria. Nick tells Malou that work permit quotas are used up, but his solicitor Heath came up with a scheme whereby she'd marry for resident status.
Johnny and his colleague Mike discuss Nick's offer. Mike is sceptical - he believes that it's a scam that will ensure girls can't be deported if they're caught working London streets.
Johnny is summoned to pick up a client, who turns out to be Heath. He meets Malou in the waiting room and they decide to go through with it. Mike drives them to the registry office and recognises Aggie as a former prostitute. Afterwards, Aggie takes Malou back with her.
Malou discovers a hidden doorway separating the respectable half of Aggie's house from the brothel. She glimpses Vicki 'entertaining' a client, before picking up a second man from the street. She frantically packs her things, but Nick arrives to prevent her departure. He tells her that she's being groomed for his best clients... and himself.
Johnny demands Nick's address from Heath, who rings Nick after he leaves. Johnny drives up at a derelict building and is beaten up. He tells his colleagues, who agree to help.
Nick introduces Malou to Maria, whose face is scarred with acid. He offers her a drugged cigarette, which gives her nightmares, and wakes up to find Nick threatening to frame her for murder. He puts her out on the streets, arranging for a henchmen to be her first 'customer'.
Vicki, desperate for Malou not to end up like her sister, tries to give her advice, but before the 'deal' can go ahead Johnny and Mike arrive. Mike is badly beaten but Johnny and Malou escape.
At Johnny's home, Malou recounts her ordeal, and he admits he's fallen in love with her. Vicki tells Mike that she's only a prostitute to raise money for Maria's hospital bills.
The next day, Johnny and Malou behave like a married couple, with her seeing him off to work. But when he tries to ring her later, he gets no answer. Rushing back home, he finds Nick in his house. Mike arrives to find the place trashed, Johnny on the floor and Malou gone.
Aggie urges Nick to send Malou back to France. Vicki says she's temperamentally unsuited to be a high-class prostitute. Nick says he'll get rid of her another way. Vicki hears screams from next door - Maria has killed herself.
A distraught Vicki calls Johnny and gives him Aggie's address. He gains entry by pretending to be a client, breaking Malou's door down as Mike and the cabbies storm the building downstairs. Vicki locks Nick into an upstairs room, soaks a bed with spirits and sets it alight.
Spotting the smoke, Mike and Johnny rush upstairs. Nick breaks out of the room, pushes Vicki aside and climbs onto the outside balcony. Mike rescues her, and Johnny insists on helping Nick. The two men grapple, and Nick falls to his death. Johnny is rescued by a fireman, and tells Malou that it's all over.
