The Boy, a dreamer who fancies himself a Don Juan, rejoices when his mother at last allows him to change from his knee breeches to long pants. He goes out for a bicycle ride to show off to his neighbors that he is now a man, and while out, he encounters the Vamp, a beautiful crook being sought by the police for smuggling "snow." She is amused by the Boy and flirts with him while he rides around her car trying to impress her. He is called back home to talk on the phone with his girl friend Priscilla, and after he hurriedly hangs up on her, he rushes back out to the Vamp. She is gone, however, and has accidentally left behind one of her unsigned love letters, which the Boy mistakenly assumes is for him. He thinks that the Vamp wishes to marry him, and his parents, who know nothing of the Vamp, naturally assume Priscilla is the focus of his desire to get married. His parents arrange for the young couple to be married at once, but the Boy, intent on a passionate life with the Vamp, decides that he must kill Priscilla to avoid marrying her. He takes her for a walk in the woods, but his incompetence prevents him from shooting her, and he ends up getting caught in a bear trap, from which Priscilla rescues him. The Boy then discovers that the Vamp has been incarcerated for her crimes, but his attempt to rescue her is complicated by his run-ins with a mannequin police officer, and then a real police officer. The Vamp gets into a fistfight with the woman she holds responsible for her arrest, and then shoots her husband. The Boy is jailed, but when he is released, he thinks of his mother and Priscilla and rushes home to them.