It is the War of 1812 and American Naval Lieutenant Darby Holmes is duty bound to cruise the waters of the North Atlantic in an attempt to keep enemy vessels from America's shores, when he encounters a mysterious black ship and a distress signal from a beautiful woman trapped below deck. Pirates have captured Margarita Vicente's ship on her voyage to Los Tortugas after the death of her mother and she fears all is lost, until the handsome Lieutenant comes to her rescue and eagerly agrees to escort her to her new home. But duty forces Darby to leave Margarita on the island with indifferent relatives who appear guarded and subdued and an overseer whose wicked gaze follows Margarita's every move. Margarita longs for Darby's return as her nights are interrupted by unexplained noises and glimpses of a phantom ship in the harbor. To her horror, Margarita realizes that she has unwittingly stumbled into the midst of a covert operation and uncovered a secret the inhabitants of the island plan to keep hidden and one that now threatens her very life.