Obstetrician So-young is happily married to university professor Ji-seok. One day, however, So-young realizes that Ji-seok is having an affair with his student Su-ji when she drops by his office. Angry and despairing, So-young unleashes an elaborate plot to befriend Su-ji, beginning with spying on her in yoga class. Without knowing So-young's true intentions, Su-ji takes to her, and as Su-ji's affection toward So-young grows, So-young's rage morphs into sympathy. Amid the confusion she has created, So-young decides to make a choice: to accept either Su-ji and her genuine friendship or keep her philandering husband Ji-seok in her life.