Young-jin is feeling blue because his wife Ji-eun is not enjoying sex. One day, his high school friend Seung-cheol moves in next door. His friends wife, So-hyeon, is a very sexy woman and has an open mind to an open relationship. Impressed by her, Ji-eun talks frankly with her about the couples concern and So-hyeon suggests a kind of sex therapy. Let's swap husbands for 1 week!