Sun-jung, a senior instructor who doesn’t care about affair with pretty girls, and Myung-jin, a young instructor who spends his days picking up trash because of such an idiot-like senior. Myung-jin falls in love with a beautiful student ‘Yura’ in an advanced class where he accidentally entered as a pinch hitter, and afterward, he sees Sun-yung, who starts flirting with Yura, like a thorn in his eyes… Under the cool swimming pool, a secret love game begins...