Yuri has been married for five years and is far more active than her appearance suggests, with running and marathon events among her favorite pursuits. One day she falls and injures herself during a run, and the man who helps her eventually becomes her lover. Accustomed to being treated like a housekeeper by her husband, she is moved by the stranger's kind, gentlemanly care and crosses the line. Once awakened, her desire for an affair refuses to slow down, leading the two of them to take a hot-spring trip together.