As Nathan Detroit, a seasoned gambler, finds himself under increasing pressure from Lieutenant Brannigan's relentless crackdown on illegal craps games, he is torn at a critical juncture in his life. The authorities' intimidation tactics have driven him out of his usual haunts, leaving him frantically searching for a new venue to host his game. The Biltmore garage offers a glimmer of hope, but securing the required $1,000 security deposit feels like an uphill battle given his currently precarious financial state.
On the personal front, Nathan's long-time fiancée, the alluring Miss Adelaide, is exasperated and demands to know when they will finally tie the knot after an engagement that has stretched over 14 years. Her yearning for a settled life starkly contrasts with Nathan's life as an illegal gambling operator, forcing him into a difficult position between his obligations.
In his quest for a solution, Nathan reconnects with the enigmatic Sky Masterson, a gambler known for his avid willingness to wager on anything. In a daring gamble, Nathan proposes a high-stakes bet: he will attempt to persuade a woman of his choice to join him for dinner in Havana, the city famous for its invigorating rhythms and lively nightlife. The woman he picks? The dedicated Sergeant Sarah Brown, who fervently opposes gambling as a mission sister at the Save a Soul Mission.
Sky, always the smooth talker, agrees to the wager but adds a twist of his own: he will gather a dozen sinners to attend the Mission's Thursday-night meeting in exchange for Sarah's agreement to join him on his Cuban expedition. General Matilda Cartwright, the zealous leader of the Mission, is in desperate need of increased attendance and is willing to overlook her morals if it means salvaging her beloved mission, even if it means teaming up with someone like Sky.
As the pair heads off to Havana, they find themselves swept up in the vibrant city's atmosphere, filled with salsa music and secrets lurking around every corner. Meanwhile, back in New York, Nathan must face the consequences of his audacious bet, including the unexpected arrival of Big Jule, a fearsome mobster, and the persistent presence of Lieutenant Brannigan, who is hot on Nathan's trail.
Amidst the confusion, the chemistry between Sarah and Sky intensifies. Yet, their budding romance faces challenges upon their return to Broadway, where they encounter the Save a Soul Mission's band parading through the streets, accompanied by the blaring sirens of approaching police. Nathan and the gamblers hastily retreat through the back of the empty Mission, but not before Lieutenant Brannigan arrives, determined to end their illegal activities for good.
As tensions escalate between Sky and Sarah, the stakes of their agreement weigh heavily on Sky's conscience. His uncle, Arvide Abernathy, serves as a stark reminder of his commitments, warning that failing to deliver will tarnish his reputation throughout the city.
Meanwhile, Nathan continues to run a high-stakes crap game in a damp, ominous sewer tunnel. Big Jule, suffering from a string of misfortunes, resorts to cheating, brandishing a revolver at his hip. Sky steps in to neutralize the situation, tossing Big Jule to the ground and relieving him of his weapon. Reeling from Sarah's rejection, Sky weaves a tale of losing the bet to take her to Havana, then unexpectedly presents Nathan with a $1,000 payment.
Flush with cash from Big Jule's generosity, Nathan proposes a rematch against his former adversary. However, Harry the Horse interjects, revealing Big Jule's inherent dishonesty renders him incapable of fair play. Inspired by this insight, Sky concocts a daring new bet: if he wins, everyone will attend a prayer meeting at the Mission; if he loses, each player receives $1,000.
As the doors of the Mission creak open just as the gamblers prepare to gather, Sky emerges victorious, leading to an unanticipated congregation of "sinners," though many express little true regret. Among them, Nicely-Nicely Johnson captivates attention with a vivid dream he recounts, which resonates with the Mission's values.
When Sarah learns of Sky's purported loss in the Cuba bet—a lie that she knows is fabricated—she rushes to make things right. Ultimately, Times Square transforms into a stage for dual celebrations as Sky exchanges vows with Sarah, while Nathan and Adelaide stand alongside them at the altar. Meanwhile, Nicely-Nicely beats a cheerful rhythm on his bass drum as part of the Mission's vibrant marching band.
