As Spain prepares an armada to invade England, British privateer Geoffrey Thorpe (Errol Flynn) embarks on a mission to loot Spanish ships. When he captures the vessel carrying ambassador Don Jose Alvarez de Cordoba (Claude Rains), the dashing captain falls for his niece, the beautiful Dona Maria (Brenda Marshall), who settles comfortably in England. Dedicated to protecting British interests, Thorpe heads out to sea on a dangerous expedition that may determine the country's fate.