In this Italian swashbuckler ruthless pirates threaten the rule of the Doge of Venice. Fortunately, his brave son puts on a mask, calls himself "The Lion of St. Mark," and rallies together a regiment of mercenaries to stop them. After a few skirmishes with the pirates, the Lion finds himself falling in love for a female pirate. When his mercenaries capture her, he must save her. The grateful woman offers her thanks, but refuses to give up on her pirates. When she learns the Lion's real identity, she rethinks her position. Meanwhile the pirates are vanquished, and the hero's uncle adopts the pirate woman so that she and his nephew may continue their courtship.