A man accidentally finds himself alone with his wife's mommy friend at a hot spring inn in a mixed bath. He gets an erection, knowing it's wrong, but he tries to masturbate unnoticed, but ends up being found out. However, rather than expecting to be scorned, the mommy friend seems to be happy to be seen as a sexual object and wants to watch him masturbate. Then, seeing the man's bare penis and getting excited by himself, her breath gets heavy and she can't help but reach for his penis...