During spring break, Saki's son Yuuki is invited by his classmate Masaru's mother Yurika to go on a hot spring trip with her. In fact, Yuuki has always admired Yurika's beauty and sex appeal. At the inn, he finally gets to see Yurika naked thanks to the mixed-bathing hot spring. Still excited, Yuuki sneaks into Yurika's bed and rapes her. His mother Saki finds out about their illicit relationship, and Saki, who loves Yuuki, becomes aroused...