To repay her husband's debts, married woman Nanako begins working at a hot spring inn deep in the mountains. Upon hearing rumors of the inn's dangerous reputation and feeling guilty for making Nanako shoulder her brother's debts, her sister-in-law Reiko rushes to the location. However, what awaits Reiko is Nanako bound in hemp ropes, suffering in agony. Shocked by the sight, Reiko resolves to offer her own body in Nanako's place. Yet the sensation of the ropes coiling around her groin gradually erodes the sisters-in-law's composure, unraveling their restraint.