Jae-hoon (starring Kim Rae-won), whose heart is broken by his ex-girlfriend, wakes up in the morning hungover as always, to find that he talked on the phone with someone unknown last night for more than two hours. Soon, he figures out that someone was Sun-young, his colleague from work, who just joined his team and introduced herself to him before less than 24 hours! Meanwhile, Sun-young (starring Kong Hyo-jin) is undergoing a messy breakup.