A woman getting wet on a pleasure boat

Eriko (Yamaguchi) marries her husband, who runs a cruise ship and guesthouse, but loses her husband and becomes a widow. Eriko is unsure whether to leave home or not, but her mother-in-law, Kiyoko, is plotting to make either her second or third son her husband... One day, Shinzo, the third son, is ordered to give a massage to Eriko, who hurt her lower back. Eriko gets into a naughty mood as her body is massaged and she ends up having a relationship with Shinzo. The widow's desires are in full swing and she ends up on a pleasure boat...