Yuri has been married for five years and is far more active than her reserved appearance suggests. Her latest passion is running, and she even competes in marathons. One day, she carelessly falls and injures herself during a run, only to be rescued by the man who later becomes her lover. Her husband usually treats her like a housekeeper, so the other man's kind, gentlemanly attention touches her deeply enough to make her cross the line. Once her desire to cheat starts running, nothing can stop it, and this time the two lovers set off on a hot-spring getaway together.