Married woman Aki is lured by her lover to a secluded hot spring inn deep in the mountains. This inn is notorious for voyeurism and orgies, attracting many guests seeking such thrills. The man who brought Aki has sadistic intentions, aiming to train and dominate his submissive lover. To further humiliate her by exposing her as a plaything for other men, he plots to involve her in group sex with the other guests.