Paroled gangster Johnny Eager pretends to be an honest taxi driver, but actually runs a large gambling racket. Leaving the office of his parole officer, Mr. Burns, Johnny encounters society girl Lisbeth Bard. They are attracted to each other, but after Johnny leaves, the skeptical Lisbeth goads Burns into paying a surprise visit to Johnny. Although he supposedly lives with his cousin, Johnny actually lives in luxurious quarters at a closed dog track. After being tipped off by someone in Burns's office, though, Johnny arrives at his cousin's modest apartment just in time. He becomes even more intrigued with Lisbeth, who is the opposite of his current girl friend, Garnet. Later, at the track, Johnny begins to suspect that Lew Rankin, a childhood friend, is cheating on him and has him followed. That night Johnny and his underling, Jeff Hartnett, a brilliant, but cynical alcoholic, check up on Lew at Tony Luce's gambling house. Johnny is surprised to find Lisbeth, whose drunken escort owes Tony money, in the office. After Tony confirms Johnny's suspicions about Lew, Johnny leaves with Lisbeth. Late that night, when Johnny takes Lisbeth home, he learns that her stepfather is John Benson Farrell, the crime busting district attorney who is keeping the dog track from reopening. Farrell and Jimmy Courtney, an aristocrat who loves Lisbeth but recognizes her need for excitement, warn Johnny about hurting her, but he pretends to be just an honest parolee. The next morning, Johnny sends Garnet to Florida, lying to her that he will join her later. Jeff chastises Johnny for his cold-blooded treatment of Garnet and says that the only reason Johnny keeps him around is that "even Johnny Eager has to have one friend." Later, Farrell comes to the track to threaten Johnny and says that he would do anything to protect his daughter. One night, Lisbeth visits Johnny and makes him admit that he loves her. Just then, Julio, one of Johnny's henchmen, comes in, brandishing a gun. Johnny knocks it away, and in a struggle, yells for Lisbeth to pick it up. Fearing for Johnny's life, she shoots Julio, then becomes hysterical when she realizes that she has killed him. After Johnny rushes her out of his apartment, Julio gets up, joking about his acting skills. Johnny admits to Jeff that he feels badly about Lisbeth's obvious pain, but thinks that she will soon get over it. Later, he and Jeff crash a poker party at Bill Halligan's, a politician on the take. Pretending to be drunk, Johnny goes into a bedroom to sleep, then sneaks out the fire escape, meets Lew, kills him, then goes back to the poker game. Soon Farrell goes to see Johnny and tells him that Lisbeth has been in a state of shock. Seeing his opportunity, Johnny says that Lisbeth killed Julio, but he will keep things quiet if the track can reopen. Feeling that he has no other choice, Farrell acquiesces. On opening night, Johnny runs into Mae Blythe, an old girl friend who is now happily married to a policeman. As a favor, she pleads with Johnny to use his influence to have her husband, who wears badge 711, transferred back to a beat closer to home. Johnny says he cannot help her, even though it was Johnny who had her honest husband removed from his old beat because he caused problems for Johnny's rackets. Back in the apartment, Courtney agrees to give Johnny $500,000 in cash if he will close the track and go away with Lisbeth. When Jeff tells Johnny that he does not understand because Courtney is acting unselfishly, Johnny slugs him. Jeff leaves, but soon returns because, he says, he is weak. After apologizing, Johnny takes Jeff with him while he visits Lisbeth. Seeing how distraught she is, Johnny begins to understand what love and decency are. When she declares that she will give herself up after Johnny's parole is over, he tries to tell her about the ruse, but she thinks he is merely being kind. After saying that he truly does love her, he leaves and tells Jeff that he plans to bring Julio to her. Realizing how dangerous the situation is for Johnny, Jeff tries to dissuade him, but Johnny soon finds Julio at Halligan's. Johnny calls Courtney and tells him to bring Lisbeth to him, then tells the reluctant Jeff to get loudly drunk and go bar-hopping. When Lisbeth and Courtney arrive, Johnny informs her that Julio will be arriving soon, then tells her to go to Courtney after they split up. Because she becomes hysterical and says Johnny is lying that he no longer loves her, Johnny slugs her, and after she passes out says "so what if I was." He then tells Jimmy to get her away and never tell her what he just said. After they drive off, Halligan and his men come outside and have a deadly shootout with Johnny, who is then mortally wounded by a policeman. Jeff returns and takes the dying Johnny in his arms. When the policeman, who wears badge 711, asks who he just shot, a grief-stricken Jeff says "this guy could have climbed the highest mountain in the world if he had just started up the right one."