Masa goes to Mika's house for the first time in three years to see his mother's beautiful and charming sister, Mika. What he sees there is his mother, Hisae, entangled in a lascivious embrace with Mika. The next day, when he tells Hisae about it, she tells him of the mothers' plan: "When things got to this point, we all wanted to have some fun together." The mothers no longer need to hide anything, and the son learns the truth. With Mika's son in the mix, a massive incestuous affair between mother and son begins...