Park Hayeon couldn't believe how everything changed in a night. A few hours before the fight, her relationship with Lee Sungyeol was completely okay. But then they stopped talking because of their own pride. Sungyeol, who was going to Australia with his parents, was really disappointed in the girl. He left her with nothing except a slap and yells. 

Hayeon, who was able to move on from Sungyeol, got a new boyfriend while Sungyeol couldn't even go a day without thinking about her. No matter how far she was, for him, it would always be her. He regretted everything he said to her at that night, feeling so stupid for letting her go. 

Three years after it, Sungyeol came back to Korea and met Hayeon who already had a boyfriend. How would he react to the painful fact that she had already moved on from him? Would he stop fighting for her and give up after three years of missing her?