The three thirty-something wives were classmates from their university days. Although they lead fulfilling lives, they are dissatisfied with their sex lives with their husbands. One wife accidentally meets her ex-boyfriend from university on a trip to a hot spring, and they end up laying naked together in a mixed outdoor bath. When the three cheating wives are joined by four husbands who are relaxing on their trips, the burning passions go nonstop! At the inn, each of them indulges in extramarital sex, and it eventually develops into a huge orgy with seven men and women mixed together.