Arnolphe, middle-aged man-about-town, has deliberately kept his young ward, Agnes, innocent of the ways of the world. Now she is 18, he intends to marry her, but hasn't told her yet. She meanwhile has fallen for young Horace, newly in town. There ensues a cat-and-mouse game with each of the lovers innocently revealing their secret plans to Arnolphe, who systematically thwarts them while pretending to be Horace's ally and keeping Agnes under ever closer guard. Eventually Horace's father arrives in town intending to marry him off to a friend's daughter, who has been brought up by a guardian. Arnolphe heartily endorses this scheme as a way of removing Horace from the scene, only to discover that the intended bride is Agnes herself.