Staff heard rumors of a secret hot spring and stayed overnight to film on location, where they found a notoriously lewd married woman enjoying mixed bathing. The spring has a unique custom requiring both men and women to wear fundoshi before entering, but male guests are quickly sucked off upon arrival. The crew learns of this tradition and joins in, leading from aggressive blowjob sessions straight into a 4P. As filming progresses, the most glamorous shaved-pussy wife is interviewed and brought on board, then tormented with an electric massager, climaxing repeatedly in obscene poses. Meanwhile, another crew member is shown in a room with two married women engaging in lesbian play, having his toes licked and semen drained. A steamy, erotic scene unfolds at the hidden spring, woven from bizarre customs and lascivious developments.