A trendy dark fitness studio opens near Maki Hojo's home, and she joins hoping to relieve stress. In reality, the crooked gym secretly spikes married women's drinks with a drug said to increase sensitivity a hundredfold before exploiting them. After the first dose leaves Maki intensely aroused, she mistakes it for a workout high and tries to seduce her exhausted husband, only to be rejected. Still unaware of the truth, she returns to the studio, where the predators finally close in on her.