Mai is frustrated by her sex life with the boyfriend she hopes to marry. When her pent-up desire reaches its limit, she sleeps with a kind man who attends her swimming class. It is supposed to be a one-time affair, but her body soon begins craving her lover instead of her boyfriend. After lessons, the young, slender and beautifully toned instructor loses all restraint in an empty pool, moaning and crying out as she climaxes again and again with the man her partner knows nothing about.