In the year 1848, Vance Colby, played by Dale Robertson, returns to New Orleans after spending four years away from his hometown. He is quickly summoned by his father, a notorious gambler, who calls him aboard his riverboat. During this encounter, a fellow gambler named Gottfried accuses Vance of cheating at cards. In a swift and brutal confrontation, Vance defends himself and beats Gottfried into submission. However, as Vance turns away, Gottfried attempts to attack him with a baling hook, forcing Vance to defend himself once more. Luckily, Melanie Barbee, played by Debra Paget, the daughter of Captain Antoine Barbee (played by Thomas Gomez), steps in just in time to save Vance from further harm.
Later, on land, Vance encounters Ivette Rivage, portrayed by Lisa Daniels, after her carriage's horse goes lame. He helps her and soon finds himself at the Rivage plantation named Araby, where he meets her brother André Rivage and her fiancé Claude St. Germaine, played by Douglas Dick. The mood shifts when they discover that Vance is Chip Colby's son, which causes André and Claude to grow noticeably cold and suspicious toward him.
As Vance departs the plantation, André quickly takes action, sending his henchman Etienne, played by Peter Mamakos, along with two others to ambush him. During this attack, Etienne throws a knife that pierces Vance's side, but Vance retaliates by shooting Etienne in the arm and manages to escape in a small boat. His wound is treated by Captain Barbee, who had earlier saved him aboard the riverboat, revealing a past connection: Barbee once owed his vessel's survival to Vance’s father after a near ruin caused by a cheating card sharp.
Vance then seeks out his deceased father, only to find a coffin in his place. He learns from Police Commissioner Robert Renard, played by Henri Letondal, that his father was accused of cheating and was shot by Ivette's father, Rivage, played by Woody Strode. The story is supported by casino owner Nicholas Cadiz, played by John Wengraf, and a waiter named René Garonne, played by Jay Novello. Vance writes down their names on a three of spades playing card—symbolic of the dangers and treachery he faces.
Determined to uncover the truth, Vance kidnaps Garonne and pressures him into revealing the real story. Garonne confesses that Rivage, Colby, and others were involved in a game of 21 (blackjack) at Cadiz's casino. Rivage lost his new riverboat, the Baton Rouge, in a high-stakes game to Chip Colby, then insisted on one last hand, wagering Araby against the boat. After Rivage's defeat, his rage boils over, and he shoots Colby. To cover his tracks, Cadiz then plants a marked deck into Colby's winning hand. Garonne also mentions that Rivage, Claude, Cadiz, and Colby were partners in the riverboat operation. However, Garonne is abducted during the night, leaving Vance with crucial information but no concrete proof.
To further incriminate Vance, his enemies plant Garonne’s body in his hotel room, but Melanie notices and becomes suspicious. Her suspicions lead her to alert Captain Barbee. Meanwhile, the antagonist Claude St. Germaine is caught in the act of framing Vance, ultimately falling to his death during a confrontation.
Vance then devises a daring plan, with Barbee posing as a wealthy plantation owner, to expose Cadiz cheating at his casino. As Barbee begins winning, Cadiz sends in a ringer with a secret code to switch to marked cards. Detecting this, Barbee signals Vance, who arrives with Commissioner Renard. With evidence of cheating in hand, Renard revokes Cadiz’s casino license. Enraged, Cadiz strikes Vance, leading to a tense pistol duel. Vance aims to spare Cadiz if he confesses the truth about his father’s death, but Cadiz, instead, draws a derringer and is shot by Vance.
Resolutions arrive as Rivage, in desperation, challenges Vance to a final game of 21, with both wagering their halves of the riverboat. Vance wins the game, and Rivage, then drawing his cane sword, attempts to attack him. Melanie intervenes by throwing Vance a sword, and a fierce duel ensues. During the fight, Etienne tries to strike, but Josh defuses the situation. Ultimately, Vance manages to kill Rivage in the duel.
In the aftermath, Vance returns the deed to Ivette Rivage, who expresses her gratitude and invites him to stay with her. However, Vance reveals that he has other plans, which include Melanie, suggesting a new beginning and hope for the future, carrying the weight of past betrayals and sins but also the promise of redemption and love.
