Bora, a 17-year-old girl, is tasked by her best friend Yeon-du to gather information about a boy named Baek Hyun-jin while Yeon-du is away in the US for heart surgery. In order to do so, Bora decides to get close to Baek's best friend, Pung Woon-ho. However, as she delves deeper into her plan, things take an unexpected turn, leading Bora to experience the fever of first love in 1999, a year before the new century.