Mika is an ordinary housewife living with her husband, Masaki. Masaki is a busy salaryman, and Mika, dissatisfied with their lackluster sex life, satisfies her desires through masturbation. One morning, as Mika sees Masaki off at the door, Ikuzo—an elderly man living alone next door—strikes up a conversation. That afternoon, Ikuzo enters her home under the pretext of checking the water pipes and secretly plants a listening device. At night, he eavesdrops on the sounds of Mika indulging in masturbation...