Dorothy has been brought up to appear in public with Balzamo, a hypnotist, who claims to be her guardian. By constantly subjecting her to this hypnotic influence, he has weakened Dorothy's will-power. The dual personality which lurks in everyone becomes so strong that it insists upon manifesting itself to the world as another personage in the bodily form of Dorothy. This personage calls itself Becky and is fully cognizant of Dorothy, whom she hates, whereas Dorothy is not so truly aware of Becky; she does not remember all that Becky has said and done. Dr. Emerson, a specialist in nervous diseases, who is much interested in hypnotism, has a young assistant, Dr. John Arnold, who possesses great hypnotic power. Dr. Emerson urges the development of the power, arguing that it can be used for good as well as evil purposes. Dr. Emerson tells Dr. Arnold how his own life was wrecked years ago by a hypnotist, who induced his wife to leave him and take their little child. The wife died deserted and the doctor has never been able to find the child or the hypnotist whom he knew as Schwartz. Balzamo, as Dorothy grows older, becomes attracted to her and decides to discharge the older woman that is working with him and make Dorothy his star performer. Dorothy, when she hears this, becomes for the first time visibly Becky and runs away. She has various experiences earning her living, always getting a position through her sweetness and amiability as Dorothy and losing it through the ugliness and malice of Becky, who appears more and more often as she grows stronger. Dorothy becomes companion to Dr. Emerson's sister and begins to fight Becky. She visits the Doctor's sanitarium and there meets Dr. Arnold, who falls in love with her. There also, Becky insists upon making her appearance. Dr. Emerson recognizes it as a case of dual personality which he is anxious to study to help Dorothy. But Becky is impossible; she will tell the Doctor nothing and hates Dorothy because Arnold is in love with her. Becky takes malicious delight in making everybody miserable. Balzamo, who has traced the girl from place to place, comes to town to get her and to give a performance. Dorothy, frightened at the sight of him, tells Dr. Emerson everything. The two doctors make up their minds that they must kill Becky to free Dorothy and then free her from Balzamo. The fight begins and after a hard struggle Arnold kills Becky and defeats Balzamo and making him confess that Dorothy is Dr. Emerson's daughter. Balzamo is sent away with his power broken. Dorothy, knowing that Becky is no longer to be feared and that Balzamo is out of her life, yields herself willingly to Arnold's love.