In 1933, an older man named Chaney [Charles Bronson] watches a bare-knuckled street fight, where bets are laid on the outcome. The fighter, backed by the cocky, fast-talking "Speed" [Strother Martin], loses badly, and Chaney talks a very skeptical Speed into letting him take on the winner. Chaney bets all of the six dollars he has on himself and quickly dispatches his younger opponent, setting the tone for a brutal, high-stakes run. Chaney and a suitably impressed Speed travel to New Orleans to match Chaney against local fighters at long odds, recruiting genteel drug addict Poe as a cutman. Between fights, Chaney finds a down-on-her-luck woman named Lucy Simpson [Jill Ireland] to sleep with, a relationship that hints at the loneliness and instability perched beneath the surface of their hard-edged world.
Chaney easily disposes of his next opponent, a Cajun, showcasing a growing confidence that unsettles those who bet against him. When Pettibone, the loser's sponsor, refuses to pay off his bet, Chaney advises Speed to retreat for now, though he encourages a return when the odds swing back in their favor. That night, Chaney sneaks into Pettibone's honky-tonk joint, brands a gun, flattens the hood's goons, and shoots up the place, seizing the winnings from Pettibone after clubbing him with the pistol in a display of cold efficiency.
For the next fight against local brawling champ Jim Henry, sponsor/fish tycoon Gandil unexpectedly raises the stakes to $3000 instead of the usual $1000. To cover the shortfall, Speed secures a loan from a gang of local mobsters headed by Doty, a move that tightens the noose around Chaney’s plans. Chaney wins this fight handily, but gambling addict Speed blows all his winnings in a backroom crape, leaving him unable to repay the loan sharks and pulling Chaney deeper into a dangerous savings-and-debt spiral.
Afterwards, Speed and Chaney disagree about selling a piece of Chaney to Gandil. Gandil instead pays off Speed's debt and takes him hostage, forcing Chaney into an impossible choice. Chaney must wager his entire winnings to take on a prize fighter imported from Chicago named Street [James Coburn], or Speed will be killed. Chaney is torn between rescuing Speed from his own folly and preserving his hard-won independence, and Poe pleads for a choice that would preserve some humanity amid the violence. His relationship with Lucy ends as she finds a new man who offers more stability and has a “real job,” a stark reminder of what’s left behind when one keeps chasing the next fight.
Chaney steps into the arena for the bout with Street, the Chicago fighter proving a formidable foe. The match escalates as Chaney gradually gains the upper hand, testing his endurance and nerve against a man bred for this brutal art. When Street is knocked down and on his hands and knees, Gandil slams two metal cylinders on the ground for him to wrap his fists around, but Street is too proud to cheat. Chaney endures the grit and intensity, and with a final, decisive effort, finishes Street off to claim the victory he has staked everything on.
In the aftermath, Chaney shares a generous cut of the winnings with Speed and Poe before leaving town, choosing flight over fame. He leaves instructions for Poe to take care of his stray cat, a small, lingering detail that underscores the odd, fragile humanity that persists even in a life defined by risk, blood, and the relentless pursuit of a bigger score.
