Lorenzo, a gambler and dance hall owner, lures young Mabel Whitney from her family to work in his establishment. Years later, she is discovered there by Major Dean, a U.S. Army surgeon, who is interested in the power of mental telepathy and "thought-suggestion." Drawn to both Mabel's beauty and her susceptibility to hypnotic influence, Dean uses his concentration to stop her from drinking from a glass she has raised to her lips. Just as he is thinking of a way to expel Lorenzo's influence from her mind, a fight breaks out in the dance hall, all the lights are extinguished, and a bullet grazes Mabel's temple, knocking her unconscious. Dean carries her home, and when she awakens the next morning without any memory of who she is or how she got there, he convinces her that she is his daughter. Hoping that a wholesome and moral environment will rehabilitate her, Dean takes Mabel with him when he is transferred to a new base in the West. Lorenzo learns of her whereabouts and follows, in order to manipulate her again, but Dean's powers of telepathy are able to protect her. Unable to recognize Lorenzo, Mabel is repulsed by him, and when he tries to kidnap her, she is rescued by a young lieutenant, Sibley, who falls in love with her. Meanwhile, Whitney, a sergeant under Dean's command, recognizes Mabel as his long-lost daughter, and although he does not know who lured her away, he has promised to kill the man if he ever finds out. As Lorenzo and Major Dean continue their fight for Mabel's mind, Whitney discovers Lorenzo's identity and strangles him, but not before Lorenzo wounds him with a fatal shot. Mabel, sleeping nearby, awakens with a start, and tells Dean that a bad dream has caused her to sleepwalk. Despite being told of Mabel's past, Lieutenant Sibley proposes marriage and she accepts.