Ace Corbin [Cary Grant], a charming Chicago gangster, is acquitted of murder charges that were framed by Pete Manning [Jack La Rue], setting the stage for a fresh start in California. On the train to the West Coast, he crosses paths with Eleanor La Velle [Benita Hume], a gambler's girlfriend, and the pair tumble into a tentative romance while both keep their true identities hidden.
In Southern California, Eleanor learns that her lover Joe Burke [Arthur Vinton], the owner of the Casino Del Mar steamship—operating legally beyond the three-mile limit—is in debt for $9,000, a consequence of Manning's thugs disrupting his business. Despite the danger, Eleanor chooses loyalty and stays close to Joe, helping with his operation as he tries to weather the threat.
Joe and his right-hand man Blooey [Roscoe Karns] propose handing the casino over to Ace so he can rebuild the business and exact vengeance on Manning. Ace resists at first, but Manning's men escalate the pressure, pushing him toward a larger stake. When Ace finally takes the helm of the casino, he has the water taxis ferry Manning's patrons to his steamship, turning the tide of power in his favor.
The first evening aboard, Ace encounters Eleanor again, and she discovers his true identity. Though she is still in love with Ace, she remains aboard the ship, risking exposure while the casino drama unfolds under the shadow of danger. After the fire and explosion are contained, Ace and Eleanor stay on the ship through the night, growing closer, even as the threat to them lingers.
The next morning, the district attorney questions them both, and Ace uncovers Eleanor's real identity and her ties to Joe. Joe himself arrives and realizes Ace's link to Eleanor, a revelation that adds to the tension aboard the casino steamship. In the midst of a fierce storm, Joe and Ace confront Eleanor, accusing her of being a two-timer and torn between two men. Meanwhile Manning and his men infiltrate the vessel and kill Joe, a blow that intensifies the peril.
Blooey releases the anchor, and the violent seas hurl Manning and his men overboard. Ace, Blooey, and Eleanor make a perilous escape, leaping to safety with life preservers. In the end, the couple chooses to confront their future together, and Ace and Eleanor marry, closing a chapter defined by risk, loyalty, and hard-won reconciliation.
