The U.S. government sends Major Thomas Blake on a secret mission when the Bey of Tripoli starts demanding tribute from American merchant ships in the Mediterranean in the early 1800s. His pose as a Tory on the ship alienates his fellow passengers, Anne Ridgeway, and her brother Sam. Off Tripoli, the ship is captured by the Beys pirates, but Blake makes a friend of the Bey when he saves his life. Blake learns that a servant girl, Zoltah, and her friends ate plotting to kill the Bey, and that the Bey also has a spy in the State Department, Tobias Sharpe, who sends advance information about American ship movements.