UNDERWORLD U.S.A.

The 14-year-old Tolly Devlin and his mother figure (Beatrice Kay) see four hoods beat his father to death. Tolly vows to avenge his father, but he discovers that Farrar, the one perpetrator he recognized when his father was being beaten, has been arrested and imprisoned for life. Tolly becomes a petty criminal and safecracker. Many years later, during a stint in prison, Tolly discovers that Farrar is on his deathbed in the prison medical ward. Tolly manipulates his way into the room and tricks Farrar into revealing the names of the other three killers before he dies.

The remaining killers have risen to be powerful lieutenants in the crime syndicate, so Tolly works his way into their organization. In the process, he saves and then begins a romance with a low-level syndicate money-runner named Cuddles (Dolores Dorn). Becoming a secret informant for the police, Tolly ends up playing both sides in his cagey campaign to bring down the remaining mobsters. Tolly's machinations convince syndicate boss Connors to have each of the three lieutenants murdered by the syndicate's ruthless assassin, Gus.

Having accomplished his goal, Tolly plans to go straight and marry Cuddles. The police warn him that without bringing down Connors, he has no chance of getting out alive, but Tolly does not believe them. As Tolly prepares to leave, Gus arrives and informs him that Connors has assigned them to kill Cuddles and several other innocent witnesses. Tolly realizes that Connors must be stopped. He knocks out Gus and turns him in to the police, and then confronts Connors and his men. Tolly kills Connors, but is shot during the struggle. He stumbles into an alley and dies.

Tolly orchestrates the downfall of the syndicate lieutenants, kills boss Connors, but is fatally shot and dies in an alley.

The ending completes Tolly's arc from traumatized witness to avenging antihero, underscoring the inescapable violence and futility of revenge. While Tolly succeeds in dismantling the syndicate's leadership, he pays with his life, making his victory both complete and ultimately tragic.