Wife Chisato Shoda is unsatisfied with her husband's sex life. Her son Kazuya, longing for his mother, relieves himself daily through masturbation. One day, their homeroom teacher, Sasaki, visits their home and ends up sleeping with Chisato while helping out with her son. Unfulfilled by her husband's half-hearted affection, Chisato recalls her encounter with Sasaki and calls him again. Their affair gradually grows deeper.