Jae-hoon (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 (Kong Hyo-jin) is undergoing a messy breakup. At her very first day at work, she bumps into Jae-hoon while bad-mouthing her unfaithful boyfriend to break up with him! Despite the fact that they have come to learn more about each other’s love affair than work, this subtle tension and awkwardness between them did not last long. They start to pit against each other in a short time. Even while calling one another pathetic and ridiculous, they still care about each other deep in their heart…