Lucy, the young wife of Mr. George Langham, is a silly little woman, rather delicate. She has a companion, Hesther Rodney, whom she treats very thoughtlessly, though Hesther is very fond of her and invaluable to her. Lucy's mother, Mrs. De Lancy, comes to visit her. She is suspicious of Hesther and thinks her too pretty for her position and tries to rouse Lucy's jealousy. Mr. Langham's brother, Dr. Allan Langham, is very much interested in Hesther and feels very sorry for her. Mrs. De Lancy objects to his attentions to the companion and warns his brother. Allan is leaving for the city and his sister-in-law asks him to take some jewels to the city for her to be repaired. She gives him the case and he takes it to his room. That night Mrs. De Lancy and her maid, Pincher, ever suspicious, watch Hesther come out of her room in her wrapper, go into Allan's room and come out of it with the jewel case; she is walking in her sleep, but Mrs. De Lancy suspects the worst and the next morning, when the jewels are missing, she accuses Hesther. Hesther protests innocence and demands a search. They search her room and the jewels are found in her bureau. Allan guesses the truth, suggested by a newspaper article about a somnambulist who "steals" in her sleep, and pleads for time. The next night he watches with Mr. Langham, his wife and Mrs. De Lancy, and Hesther repeats the performance of the night before. Mrs. De Lancy, still doubtful, wakes her and the shock makes Hesther ill; during her convalescence she is attended by Allan, who proposes to her and wins her for his wife.