Paul Manning (Walter Matthau) is a merrily married father of one who is nevertheless fascinated by his buddy Ed's many extramarital affairs. In a series of teaching and stories, Ed gives Paul lessons in how to have the perfect affair while still being attentive of one's wife. Paul is captivated and eager, but Ed urges caution so as to perfect the technique. When he thinks Paul is ready, Ed makes him do a practice run with him standing in for the imaginary girl. Paul passes with ease, and starts his new venture on finding the perfect affair.