Flotsam, the daughter of lighthouse keeper Amos Bart, uses her experience maneuvering in the perilous New England reefs to save Mrs. Elmer, who is vacationing with her son Edward and friends on their yacht, from drowning. Edward and Flotsam spend much time together and fall in love, but when he proposes, Amos' helper, the brutish Joey Clark, who wants Flotsam, reveals that years earlier Amos murdered Edward's father. Amos, who believes that he committed the crime while intoxicated, confesses that Flotsam is not his daughter, but that of a dying woman who brought her to his wife to raise. After he tells Flotsam to go with the Elmers, Edward's jealous former sweetheart tells her about the murder that Amos committed. Flotsam returns, followed by the yacht, and she and Edward see Clark taunt Amos by confessing that he murdered Edward's father. After Amos chases Clark up the lighthouse steps, their struggle causes the light to go out.