Set in 1920s New York, the story opens with a housewarming party hosted by Larry Shaw and his wife Margaret Shaw. Amid the merriment, they cross paths with Father Gorman, a priest who grows increasingly worried about their suddenly luxurious lifestyle. Larry has just wrapped up a job for his boss, Chesty Miller, and as he pursues a bigger future, he pushes for a raise that ignites a dangerous chain of decisions.
Chesty tests Larry’s ambitions by placing him on the D and E squad—Discipline and Execute—in a bid to intimidate rival Biggie Gaines. Larry doesn’t stop at intimidation: he easily takes out Bo, the enforcer who runs the squad, and in a shocking turn is promoted to lead the unit himself, receiving a machine gun that is nicknamed the music box. From there, Larry’s rise is meteoric, and his ruthless efficiency earns him the ominous nickname The Music Box Kid as he begins to terrorize the streets of New York. The city’s mood shifts from awe to unease as the media start to pay attention, and public opinion begins to sour on the gang world.
After a brief Prohibition-era narration, a witness spots Larry and the District Attorney becomes involved. Chesty, concerned about legal trouble, provides Larry with a lawyer that helps him skate by on the lack of concrete proof. Meanwhile, Father Gorman, prompted by newspaper reports of the gang heat, goes to check on Margaret, convinced that her husband’s lifestyle is endangering her. Margaret realizes the hard truth—that their comfortable life is sustained by Larry’s gangster activities—and fear takes hold.
That night, Larry convenes a meeting with his most trusted accomplices and unveils the formation of the Larry Shaw Enterprises gang, all while Margaret listens from the kitchen and absorbs every word. Larry’s first business move is a contract proposal aimed at keeping Chesty’s gang blameless, a plan that would allow him to expand influence without taking the blame himself. The gang’s operations grow, moving money between fronts and striking at other gangs, until Larry orders the kidnapping of Pat Lamont, Biggie Gaines’ right-hand man, demanding a ransom that signals the depth of his power.
Tension with Margaret deepens as Father Gorman presses her to reveal what she knows about the gang to George Gordon, the new chief hired to bring Larry and his rivals to heel. Margaret initially resists, but she later overhears Larry’s chilling plan to kill George Gordon and to offer it as a contract to the gang leaders for $1 million. Thinking of her unborn child, she contacts Father Gorman after Larry and his crew depart and passes along the crucial information she has learned.
The climax arrives in a whirl of gunfire and police action, with Larry meeting a violent end at the hands of a pursuing officer during a scuffle. The film closes on a stark note, showing the fate of Margaret and their son, who ultimately chooses a different path and decides to become a Priest.
