As the scorching summer of 1940 envelops Fort-de-France, Martinique, Harry Morgan, portrayed by Humphrey Bogart, finds himself steeped in a profound sense of world-weariness. The captain of the Queen Conch sport-fishing boat navigates the treacherous waters of both the sea and his turbulent life amidst the backdrop of Vichy France, where the island's once-vibrant spirit is now overshadowed by an oppressive regime.
Harry's modest existence revolves around chartering his boat to tourists, alongside his loyal yet slightly confused friend, Eddie, played by Walter Brennan. Their relationship transcends mere friendship, with Harry taking on the role of a protector, safeguarding Eddie from his own personal demons.
Unbeknownst to them, whispers of dissent and rebellion are circulating among the locals, with many harboring aspirations for Free France and the hope for liberation from the choking grip of Vichy control.
One day, Harry is approached by Gérard—affectionately dubbed "Frenchy"—who urges him to use his boat for smuggling individuals onto the island in support of the French Resistance. However, Harry resolutely declines to become embroiled in the chaotic political landscape, preferring to remain an observer rather than a participant in the turmoil surrounding him.
At his hotel home, Harry encounters Marie ("Slim") Browning, a free-spirited American played by Lauren Bacall, who has recently arrived from Rio. Slim, captured by the hotel’s atmosphere, tries to escape the advances of an aggressive Johnson while confidently singing a heartfelt rendition of "Am I Blue" with pianist Cricket and his band.
As Harry closely watches Slim, he realizes that she has taken Johnson's wallet, containing a staggering $1,400 in traveler's cheques and a valuable plane ticket scheduled to leave the following morning. When Harry confronts her, demanding she return what she stole, he gains insight into the depths of Johnson's financial troubles.
Just as Harry prepares to restore the wallet to its owner, chaos erupts outside when a gunfight breaks out between police and Resistance members, spilling into the hotel. In the upheaval, Johnson is ironically struck down by a stray bullet. The authorities swiftly apprehend Harry, Slim, Frenchy, and others, leaving them in a precarious situation as their belongings are searched, resulting in the confiscation of Johnson’s wallet, Harry's passport, and his hard-earned cash.
As the tension escalates, Frenchy reveals a risky proposition to Harry: transporting Paul de Bursac and his wife Hélène, dedicated members of the Resistance, from a nearby islet to Martinique. Despite his reservations, the allure of monetary gain proves irresistible. Meanwhile, Slim's growing affections for Harry are cast aside when he uses their shared earnings to secure her flight back to America.
In the subsequent days, Harry faces a series of perilous challenges while traversing the Caribbean waters. After successfully transporting the de Bursacs, Harry's boat comes under assault from a naval patrol, leaving Paul wounded yet alive. With his resourcefulness, Harry manages to evade capture, helping the fugitives transfer to a pre-arranged escape vessel.
Returning to the hotel, Harry finds Slim lingering, her resolve to leave replaced by a newfound intent to stay with him. The de Bursacs are hidden within the hotel’s basement, where Harry must tend to Paul's injury at Frenchy's insistence. As their stories unfold, it's revealed that the couple's mission to Martinique is to facilitate the escape of a crucial figure from Devil's Island, a plan critical to bolstering the Free French forces.
Despite Paul's plea for help in this dangerous endeavor, Harry remains steadfast in his refusal to engage with the unfolding conspiracy. However, unbeknownst to them, their hotel is a hive of Vichy activity, and it is only a matter of time before the authorities act to eliminate any threats.
When the police arrive at the hotel, Harry finds himself ensnared in a precarious confrontation with Captain Renard. With unwavering determination, Harry manages to turn the situation around, neutralizing one officer and taking the Captain hostage to secure Eddie's release and the necessary passes for their escape.
With the authorities momentarily subdued, Harry, Eddie, and Slim set out to rendezvous with Frenchy and the de Bursacs at the Queen Conch, fully committed to orchestrating a daring escape for the key figure from Devil's Island—an act that has the potential to dramatically disrupt the Vichy regime’s stranglehold on the island.
