On board a British merchant ship in the 1700s, Lt. Brian Hawke endures twenty lashes, hoping the scars will falsely mark him as a deserter and allow him to infiltrate the pirate island of Libertania. Once on the island, he and fellow spies Jones and Harris are allowed entrance but forced to stand trial before the court of the Captains of the Coast, which is made up of the island's head pirates. At the trial, Hawke is shocked to see that a beautiful woman he flirted with earlier, Spitfire Stevens, is one of the captains. Pirate Roc Brasiliano, jealously recognizing Spitfire's attraction to the stranger, insists that Hawke prove himself in a fight to the death with a burly thief named Swaine. With Spitfire's help, Hawke wins the fight, and Brasiliano hires him as a navigator. As he outfits himself at the gunsmith's, Hawke learns that Spitfire is the daughter of the island's founding pirate, and that she protects her honor by killing any man who tries to touch her. Spitfire, who lives over the gunsmith's, calls Hawke into her chamber, where he notices a map drawn by her father showing the island fortifications. As he steals glances at the map, hoping to memorize it and provide the British with its information, Hawke charms Spitfire with lessons on how to behave like a lady. He soon joins Brasiliano on a raid of an Indian ship that is loaded with jewels. When the pirates attack, governess Molvina MacGregor disguises her lovely, sheltered charge, Princess Patma, as a harem girl and hides her below decks. As Brasiliano clears the boat and sets it on fire, MacGregor is forced to confide her secret to Hawke, and he bravely rescues Patma, who immediately falls in love with him. Back at the island, Brasiliano presents Spitfire with the finest of the raided jewels and proposes, but she turns him down and instead visits Hawke. He has just received a copy of the artillery map from his fellow spies, and rebuffs Spitfire's advances in order to put her in her place. During an auction of the harem girls, Hawke attempts to buy Patma, knowing that if the pirates learn she is the daughter of the Indian emperor, they will use her as bait against the British, but is outbid by a jealous Spitfire. Hawke then arranges with MacGregor to spirit the girl off the island that evening. Later that day, Spitfire offers Hawke her ship in return for passage to England, where she hopes to begin a civilized life. She informs him that she would like to trust him even though her father taught her never to trust a gentleman, and reveals that her real name is Prudence. Hawke admits that he loves her and asks her to trust him even when she is in doubt. He sneaks down to the beach that night with Jones and Harris to disable the island's cannons, after which they signal the British ship Man O' War, which is waiting in the bay. Hawke races to collect Patma, but is stopped by both Brasiliano, who believes he has come to steal Spitfire away, and Spitfire, who suspects he loves Patma. Patma, in a fit of pique, reveals to everyone that she is a princess just as Brasiliano finds the fortifications map in Hawke's pocket. Hawke and his men are tied to stakes in the tide pool and left to be eaten by giant crabs, but Spitfire takes pity on them at the last moment and unties them in secret. Dispirited, she accompanies Brasiliano onto his ship as he orders his guards to hold Patma prisoner at the bow. The British, realizing that if they harm Patma it will mean the death of every British citizen in India, are forced to hold their fire as the pirate sails off. Hawke, however, sneaks aboard the pirate ship just in time to save Spitfire from Brasiliano's clutches. After a close sword fight, Hawke kills Brasiliano and brings Spitfire on board the Man O'War. There, the only reward he requests is for Spitfire's life to be saved, and she kisses him gratefully.