A notorious raider of the eighteenth century sea lanes, Captain Vallo (Burt Lancaster), a.k.a. The Crimson Pirate, and his band of buccaneers overtake a Spanish galleon filled with guns and ammunition. When he decides to sell the stolen arsenal to rebel leader El Libre on the island of Cobra, the representative of Spain, Baron Gruda, offers Vallo 50,000 florins if he will deliver El Libre instead. Vallo is soon caught between the Spanish, the rebellion, and even the mutiny of his own men. But having fallen in love with El Libre's daughter Consuelo, Vallo gains back his crew's trust and leads the island of Cobra to freedom.