While her husband is away on a solo work assignment, Natsumi Kitahara, the stepmother, lives alone with her stepson, Yoichiro. Lately, she's become increasingly aware of his lingering glances, and finds herself seeing him not just as a son, but as a man. Meanwhile, Yoichiro is consumed by fantasies of Natsumi's sensual demeanor, drawing him deeper into desire. Their suppressed emotions entwine, escalating into an obsessive, passionate affair. A secret they must keep from her husband at all costs.