A Welsh captain (Ken Scott (actor)) and his crew are dispatched to the Spanish-controlled island of Tortuga (Haiti), where famed privateer Henry Morgan (Robert Stephens) has defected from his support of the British Empire empire and is running a strictly piratical venture, stopping any and all vessels, including English ones. Since the captain cannot attack the island without incurring the wrath of the Spanish government, he must go toe-to-toe with Morgan himself.