Strong parental objection toward her sweetheart, Jack Evans, causes Peggy Wright to make life unbearable for her brother’s friends, Professor Dinglefritz and his son, Algy, who are visiting the Wright homestead during their vacation from college. Mr. Wright is called away suddenly on business and instructs his son to keep Peggy from seeing Jack Evans. Peggy then proceeds to get even. Disguised as a little girl, she introduces herself to the professor and Algy as Peggy’s younger sister. An interesting lecture is being given by the learned professor, but Peggy is seized with a “violent” attack of sneezing and the professor is forced to abandon his work. A little later, shouts of “help” are heard and Peggy’s brother, the professor and Algy rush to the edge of the lake and are terrified at seeing bubbles forming on the surface of the water. Believing that Peggy has fallen in the lake and is being drowned, they secure a long pole and are frantically trying to rescue her, when she opens a window in the summer house and asks what they are fishing for. A garden hose, with one end in the water and the other in the summer house, reveals the fact that Peggy was just blowing through the hose and that no drowning was taking place. The would-be rescuers leave the scene, thoroughly disgusted with Peggy and her pranks. Professor Dinglefritz and Algy decide to leave this place of foolishness and return home. Peggy hears of this and enters upon a plan to prevent their sudden departure. Just as the Dinglefritzes are leaving. Peggy, having put aside the little girl disguise, enters and explains that she is Peggy and that she wishes to make amends for her younger sister’s behavior. Algy and his father fall completely in love with charming Peggy. In the quietude and shadows of a friendly old tree in the garden, the professor proposes and Peggy tells him that she will give him her answer the next evening at ten o’clock. Algy proposes the same evening and receives the same assurance. The next evening at ten finds Peggy, dressed as her younger sister again, awaiting the professor and Algy. She does not have to wait long, for first the professor appears followed closely by his son. Both are amazed at finding each other present, but still greater is their surprise when instead of Peggy awaiting them, they find her younger sister, who explains that she has just escaped from her room and wants them to help her meet her lover. Only too glad to do anything that will take her away from the spot where they were to receive Peggy’s answer, they assist her to a small boat, in which she crosses to the other side of the lake, where her sweetheart is awaiting her. Thereupon the professor and Algy hurry back to the garden, but find no Peggy. Instead, a note which Peggy has left, explains that Peggy and the younger sister are the one and the same person.