After being unjustly sentenced to prison, a doctor escapes and becomes a notorious pirate.

Late one night in 1685, Irish physician Peter Blood is called to treat his friend Lord Gildoy who has been wounded in a rebellion against England's King James II. While he tends to the injuries, the King's men burst into the room and arrest everyone there as traitors. The trial is quick and unfair. The men are sentenced to death by hanging, but the sentence is commuted when one of the King's advisors recommends selling them as slaves to wealthy landowners in Port Royal, Jamaica. Blood's arrogant attitude offends Port Royal's leading citizen, Colonel Bishop, but it intrigues Bishop's high-spirited niece, Arabella, who bids for him herself. Blood is brutally treated, but Arabella intervenes again and finds him easier work. He forms an escape plan, but on the night set for the escape, Port Royal is fired on by Spanish pirates. In the confusion, the men flee. When Bishop discovers the escape, he vows revenge against Blood. The men have no choice but to become pirates ranging through the Caribbean. During a visit to Tortuga, Blood reluctantly joins forces with the French pirate, Levasseur. The untrustworthy Levasseur boards an English ship, captures two of the passengers and holds them for ransom. They are Lord Willoughby, an emmissary of the King, and Arabella, who has been visiting in England, while her uncle, now governor of Jamaica, chases the pirates. To save her from Levasseur, Blood buys her for a handful of pearls. Frustrated, Levasseur demands a fight and is killed in the duel. Misunderstanding everything, Arabella scorns Blood. Stung by her disdain, Blood decides to return her to Port Royal, even though it means his death. In the harbor, they find a battle raging. Willoughby tells the astonished Blood that England and France are at war, and what's more, King James II has been driven from the throne and replaced by King William, who has sent Willoughby to pardon Blood and his men and offer them a commission in the Navy. With one voice, the men vote to fight the French and bravely defeat the fleet. Bishop is removed from his office, Blood is made governor, and Arabella happily agrees to become his wife.