Late one night in 1685, Irish physician Peter Blood is urgently summoned to treat his friend Lord Gildoy, who has sustained injuries during a rebellion against England's King James II. As he tends to the wounded lord, the room is abruptly invaded by the King's men, leading to the arrest of everyone inside on charges of treason. The ensuing trial is a mere sham, resulting in a death sentence that takes a turn when a palace advisor suggests selling the men into slavery instead.
In Port Royal, Jamaica, Blood's brash demeanor infuriates the local elite, Colonel Bishop, yet it captures the interest of his spirited niece, Arabella (Olivia de Havilland), who bids for him at the slave auction. Despite facing brutal treatment, Blood's circumstances improve as Arabella intervenes on his behalf. He then devises a plan to escape, but on the fateful night, chaos erupts as Spanish pirates attack Port Royal, allowing Blood and his fellow captives to flee amidst the turmoil.
Upon realizing Blood's escape, Colonel Bishop vows vengeance, compelling Blood and his companions to embrace a life of piracy across the Caribbean. During a stop in Tortuga, Blood hesitantly aligns himself with the duplicitous French pirate Levasseur. Tensions rise as Levasseur seizes an English ship, taking Lord Willoughby and Arabella hostage, while Bishop pursues them with intensity.
To rescue Arabella from Levasseur’s clutches, Blood trades a handful of pearls for her freedom. Unfortunately, misunderstandings arise, leading Arabella to scorn Blood despite his gallant actions. Burned by her contempt, Blood resolves to return her to Port Royal, fully aware that it may cost him his life.
In the chaotic harbor, they stumble upon a fierce battle. Willoughby reveals shocking news: England and France are at war, and King James II has been replaced by King William, who has sent Willoughby to exonerate Blood and his crew, offering them positions in the Navy. In unison, Blood and his men resolve to fight against the French forces and achieve a decisive victory.
As the tides of fortune turn, Colonel Bishop loses his position, Peter Blood (Errol Flynn) rises to become the governor of Port Royal, and in a twist of fate, Arabella joyfully agrees to accept him as her husband.