Mary and Masaaki are step-father and son. Mary is beautiful, close in age to him, and full of motherly love, so Masaaki tries desperately to suppress his sexual desires. However, the more he suppresses his carnal desires, the weaker his mind and body become. Unable to bear it any longer, Masaaki decides to leave home, and in the end, the three of them go on a hot spring trip together. This was supposed to be the time for Masaaki to completely cut off his feelings for Mary, but...