Mother Yumi and son Tatsuya end up having a physical relationship when father Koichi goes on a business trip! One day, as the two of them are making out, they receive a phone call from Koichi when he returns home. They know they need to stop right away, but the immoral act brings them a pleasure they've never experienced before and they can't stop. Will the two of them, who are making out more and more intensely, be able to welcome Koichi home safely?