Two couples arrive at a hot spring inn, but the husbands have secretly plotted to seduce each other's wives. The wives are absorbed in what they believe is an ordinary getaway, completely unaware of the scheme unfolding around them. Late into the night, the women are approached by their husbands' friends. Initially resisting, they gradually grow curious, their moans fading as they're led toward ultimate pleasure. A perceptive inn maid who discovers the conspiracy soon gets drawn into the web, escalating the two-day abnormal hot spring trip into even more intense territory. Amid a strange and intoxicating atmosphere, new changes begin to stir within the couples' relationships.