Miss Lillian Travers, a New York heiress, is about to visit her aunt, Miss Constancia Oglethorp, at her home in St. Augustine, Fla., and at the same time join her fiancé, Dr. Fred Cassadene. In order to discuss preparations for their coming nuptials, Lillian's coming is to be kept a secret from the doctor, who is busily engaged in a gallant flirtation with a charming New York widow. The pleasant surprise party planned by Lillian develops disagreeably when, having arrived, she hastens to the Ponce de Leon Hotel and finds the doctor making violent love to the widow. Although fearfully jealous, Lillian continues to accept the doctor's attention. One day, while sightseeing, Miss Travis finds in an old curio shop, a box, the exact duplicate of one owned by her aunt. She hurries home with her find, expecting to meet the doctor, but receives a note in which he says he will be professionally busy and unable to see her that afternoon. Piqued at her lover, she plans vengeance and is idly investigating the contents of her purchase when she discovers it contains a bottle in which are four seeds from the tree of Sexual Change, and a parchment giving detailed account of how, by taking one of them, the person will be immediately transformed into one of the opposite sex. She determines to try the effectiveness of the seeds, and if the parchment tells the truth, to get square with her lover in the guise of a man. A moment of indecision, and the deed is done. She sinks into a chair in a trance, to emerge in a few moments completely metamorphosed, and the boyhood of Miss Travis has begun. Next morning she awakes to find herself the possessor of a full-grown moustache. After much difficulty she succeeds in shaving it off, as she stills finds it necessary to be seen in feminine apparel. Joining her friends, she proceeds to make love to every female in sight, much to the discomfiture of the male members of the party. Realizing that it is improper to have a maid, Miss Travis makes Jane, her colored attendant, take one of the seeds so that she may be valeted by a person of the proper sex. The doctor, while aware that something is radically wrong with his sweetheart, persists in his love-making. Lillian, disgusted with the Doctor's amorous attentions, determines to leave St Augustine, and, by a clever ruse, just makes a train for New York. Arriving home, she sees her lawyer, turns her fortune over to a fictitious friend, Lawrence Talbot. Talbot shows up in St. Augustine with a letter of introduction written by himself and makes life miserable for the doctor by flirting with the widow and other guests in whom the doctor is interested. Circumstances arouse the doctor's suspicions regarding the integrity of Talbot, and he accuses him of murdering Lillian Travis. To save himself, Talbot confesses the mystery of the seed. The doctor does not believe him, and in a spirit of bravado, swallows one, and its action is immediate. The doctor, transformed, now makes love to all his male acquaintances. Disgusted at his actions, they call a policeman, but the doctor, scenting danger, escapes into the hotel and, to avoid the crowd following him. rushes into a strange room, where he dons a lady's dress and then hastily leaves as the owner of the room discovers him. In trying to make his escape, he is seen by his pursuers, who chase him until finally, just as he is going to be caught, he jumps into the ocean, and as he is going down for the last time, Lillian Travis awakes to find it all a dream, and with a laugh looks at the vial in her hand as Dr. Cassadene enters to pay his respects.