When painter Kate Bosworth, who is on her way to visit her cousin Freddie, misses the steamer boat traveling to an island off the coast of Massachusetts, she hitches a ride on a launch driven by handsome Bill Emerson. The launch stops briefly on the island to pick up crotchety Eben Folger, the keeper of the lighthouse on nearby Dragon Head. Determined to see Bill again, Kate talks the reluctant Eben into posing for her by offering him a ship in a bottle that he covets. One day, a heavy fog prevents Kate from leaving, and she stays a while to talk to Bill. Soon the two have fallen in love. Although Bill is leaving the vicinity temporarily for a new job, he promises to return. Kate's twin sister Pat, who is also visiting the island, meets Bill on the dock and he mistakes her for Kate. Pat pretends to be her sister and has lunch with Bill, who is totally charmed by her vivacious nature. Pat's ruse is revealed when Kate arrives, but later, learning that Bill is going to Boston, Pat takes the same train and continues her acquaintance with him. By the time Bill returns to the island, he and Pat are in love and a short time later, they marry. After her return to New York, Kate meets unsuccessful artist Karnock, who attacks her work for being stiff and repressed. One day Bill comes to town to tell Kate that he is taking a new job in Chile. Later, Karnock, who has been working with Kate, makes a pass at her. Kate realizes that she is is still in love with Bill and decides to return to the island and reflect on her life. When Kate arrives on the island, she finds that Pat is also there, escaping from her bad marriage to Bill. The twins go sailing and, during a storm, their boat crashes on a reef. Kate tries to rescue her drowning sister, but Pat's hands slip away leaving behind her wedding ring. Kate is rescued and the ring convinces everyone that she is Pat. Even after Bill returns from Chile, Kate maintains the pretense, and when she learns that Bill plans to leave her, she begs him for another chance to make the marriage work. Bill insists that Kate, whom he believes to be Pat, end her affair with Jack Talbot who divorced his wife for Pat. When Kate learns that Pat had many affairs, she is unable to face Bill and leaves for the island. There, she starts to confess her deception to Freddie, who has already guessed the truth and suggests that Kate tell Bill her real identity. She does not have to do this, however, because Bill, who has followed her to the island finally realizes that she is Kate and that he loves her.