Miki comes from her hometown to help care for her emotionally unsettled pregnant daughter. With his mother-in-law supporting the household, the husband lets his guard down, angers his wife over something trivial, and is forbidden to masturbate. A week later, Miki sees how strained the marriage has become and offers him a massage. Unaware of how sexually frustrated he is, every touch makes his erection grow. When she notices it, she blushes and makes an indecent proposal that leads them into repeated breeding sex behind his wife’s back.