On a West Indies island, former pirate Dr. Peter Blood leads a quiet life, but his occasional tending to the injuries of runaway slaves alarms his fiancée, Doña Isabela, and provokes the interest of Col. Ramsey of the colonizing British forces. British Captain Hilary Evans and Isabela's cousin, Don Ramon, report to Governor Henry Carlyle that the port of Cartagena has been sacked by a pirate ship, reportedly led by Peter. Carlyle, knowing of Ramsey's suspicions about Peter, has him arrested. When Isabela goes to Carlyle to plead for Peter, she learns that he is to stand trial for piracy. She reminds Carlyle that Peter was forced into piracy when he was falsely accused of disloyalty during the rebellion in England and sentenced to slavery in the West Indies, but was eventually awarded a full pardon by the crown. When Carlyle remains unmoved, Isabela seeks Peter's former first mate, Angus McVickers, and asks him to round up members of the old crew to band together to save their former captain. Evans takes charge of transporting Peter off the island and orders him kept in chains on board his ship, the Congo Queen . That evening, Isabela sails out to the Congo Queen to divert Evans, while Angus and his men slip aboard and overpower the crew. Once freed, Peter puts Isabela ashore, and the Congo Queen sets sail for Tortuga. As Peter puts Evans and his officers aboard a skiff with provisions, the Congo Queen meets another pirate ship captained by Peter's old friend, Tomas Velasquez. Curious about the extravagant jewels worn by Tomas' girl friend Celeste, Peter discovers the baubles were stolen from Cartagena and given to Celeste by Captain Easterling, who Tomas believes led the raid. As Peter heads to Martinque in search of Easterling, Isabela is arrested, tried and placed in prison on Puerto Bello, then awaits sentencing by the Spanish authorities for her involvement with Peter. In Martinque, meanwhile, Peter masquerades as a Dutch merchant to glean information from Easterling's girl friend Amanda, a tavern singer. Easterling sees through Peter's disguise, however, and when Peter goes to Amanda's rooms later, he finds her murdered by Easterling's henchman. Easterling confronts Peter and upon learning his identity and mission, confesses that a Frenchman named Coulevain from Santo Domingo led the Cartagena raid. Peter manages to escape, and in the struggle, Easterling shoots a guard and is arrested. Peter sets sail for Santo Domingo where, using another false identity, he seeks Madame Duval to learn of Coulevain's whereabouts. When Peter overhears that Coulevain is in need of a doctor, he offers his services, which convinces Madame Duval of his true identity. Intending to get the reward posted for Peter, Madame Duval summons the harbor police and gives him away. Disguised as the doctor's assistant, Peter tends to Coulevain on board his ship. Hearing Evans' voice nearby, Peter hides and learns that Evans is behind Coulevain's raid on Cartagena. Evans now orders the Frenchman to attack the newly arrived Spanish viceroy and seize his vast gold shipment in Puerto Bello. After Evans departs, Peter is forced to jump ship when he spots the harbor police on the pier. Reaching Tomas' ship, Peter makes plans with his friend to sneak into Puerto Bello as the military advisor to the new Spanish viceroy. In prison, Don Ramon offers Isabela a full pardon if she agrees to lure Peter to a meeting, but she refuses. Back on the Congo Queen , Peter arrives in Puerto Bello with his crew masquerading as paid British workers for the Spaniards. As the new military advisor, Peter informs the fortress commander that pirates are on the way to seize the viceroy's gold and orders the Congo Queen 's cannons hauled ashore to replace the smaller fortress cannons. Peter then orders the Congo Queen sunk in the harbor entrance and his mystified crew complies. Evans arrives near nightfall, having come over land and reveals Peter's identity to the viceroy. Peter informs the Spaniard that Coulevain is using Peter's name, but that he and Evans are the real pirates. Shortly afterward, a note from Coulevain's ship arrives, demanding the surrender of the fortress and signed with Peter's name. Evans kills the viceroy before he can begin the attack, but Peter takes command. A spectacular night battle begins, but, stopped by the sunken Congo Queen , Coulevain's ship sits directly in the fortress cannon's range and so is quickly destroyed. Peter and Evans battle each other and Evans dies falling from the high fortress walls. Later, Peter and Isabela are reunited and after receiving complete pardons, resume their wedding plans.