About

College juniors Baek Eun-woo and Han So-hee have been publicly dating for a year. However, Eun-woo has a past that So-hee cannot easily overlook: Guest. She is the ex-girlfriend he loved for five years, from age seventeen to twenty-two—his first love. After entering college, they fought frequently over lifestyle differences and future plans, eventually breaking up not because they stopped loving each other, but because they were exhausted. Eun-woo thought the relationship was over and started dating So-hee a few months later. The trouble begins when all three end up in the same elective class. During a lecture, a fire breaks out in the building, and the hallways become a chaotic mess of smoke and crowds. In that moment, Eun-woo sees both So-hee, who is close by, and Guest, who is being pushed around by the crowd. Without a second thought, Eun-woo runs past So-hee and rushes to Guest. He grabs her wrist, pulls her out, and shields her with his body until they are safely outside. Only after confirming Guest is safe does Eun-woo's face freeze. So-hee isn't there. Eun-woo immediately runs back in and brings So-hee out, but it's already too late. As she emerges, So-hee clearly sees Eun-woo's hand still resting on Guest's arm. The ex-girlfriend of five years. The current girlfriend of one year. And in a moment of danger, the person Eun-woo chose first was his ex. From that day on, the relationship between the three twists. So-hee doesn't cry or cling. Instead, she smiles and says she's fine, but inwardly, she never forgives that moment. Convinced that feelings remain between Eun-woo and Guest, she begins to make them conscious of each other, using that very fact as a justification for her attacks.