When a member of the vice squad of the New York City police department demands the name of an ambassador's wife, who is in a parked car with military attaché Major Stephen Lucarno, she runs him over and flees. Detective-Sergeant Mather, a corrupt vice squad officer, arrives on the scene, and Lucarno, refusing to divulge the woman's name, is forced to work for him. At an embassy ball that night, Lucarno bids farewell to his fiancée, Alice Morrison, and drops out of society for two years while acting as Mather's aide. Mather frames dozens of innocent girls on vagrancy charges by sending Lucarno to their rooms and, after the girls, assuming Lucarno is a gentleman, invite him in, Mather accuses them of entertaining strange men. Lucarno's self-contempt is so great he takes to drink in Greenwich Village cafes, where he meets young writer Madeleine Hunt. After Lucarno protects her from being accosted, Madeleine begins to fall for him and, one night, saves him from suicide and escorts him home. There he passes out from starvation, and she nurses him back to health. When he wakes, he insists they part anonymously, but before she exits, Mather enters, makes a pass at her and insinuates that she is a loose woman. That night, while on assignment, Lucarno is sent by Mather to an address, unaware that Madeleine lives there. When he realizes what has happened, he tells Mather there is no evidence for arrest, but after Lucarno leaves, Mather arrests Madeleine. Meanwhile, Alice's brother Tony, a judge, sees Lucarno on the street and insists he spend the evening with Alice and him. Alice deduces that Lucarno works as a stool pigeon and asks Tom to give him a job so they can resume their life together. Finally realizing that Mather can be sent to prison as an accessory to the murder of a policeman, Lucarno tells Mather he's through working for him. Madeleine's bohemian friend Josie pleads with Lucarno to testify on Madeleine's behalf, and he does so against Alice's wishes. Tony is the judge for the case and is about to find Madeleine guilty when Lucarno steps forward and admits he was a stool pigeon for Mather, who then is arrested for perjury. True to her threat that she would have nothing to do with Lucarno if his former occupation were exposed, Alice walks out of court. Madeleine and Lucarno, realizing they are in love, take a taxi to "nowhere."