Sports manager Jae-hyun (played by Yoo Yeon-seok) is a rather cynical young man. He fell in love with Soo-jung (played by Moon Chae-won) at first sight when he first met her on the KTX high-speed train in Busan. With his straightforward and uninhibited personality, he proposed to have a one-day relationship with Soo-jung. Soo-jung is an "iron wall woman" who is unwilling to give any man any chance to take advantage of her. She is quite annoyed by Jae-hyun's various unreasonable requests, but Jae-hyun is determined to win Soo-jung's heart within 24 hours. From then on, the two people with completely different ideas started a love tug-of-war.