Leslie MacLeod, a young American who has come to Scotland after buying her ancestral castle, is admired by two suitors, young nobleman Lord Glenayr, whom she loves, and Lanzana, an unscrupulous Spaniard, whom she despises. Lanzana has been promised a title by the Spanish court if he recovers a chest of jewels that sank with the Spanish Armada off the Spanish coast. Angered by Leslie's refusal to marry him, Lanzana attempts to drug her wine, but she switches glasses. Once Lanzana falls unconscious, she steals his treasure map and presents it to Glenayr. With the aid of a friend's submarine, they find the wreck, and Glenayr dives for the treasure. When Glenayr finds Lanzana there already, they struggle; Lanzana drowns, and Glenayr secures the jewels and marries Leslie.