Soo-jeong has been dating with her boyfriend for 10 years, but their relationship isn't going so well. In the day of her business trip, she finds out that her friend is getting married with her first love, so she starts to feel weird and has some thought. On the train, she sits next to Jae-hyeon who is a womanizer, he feels attracted to her and tries everything to make her fall for him. They will share the trip to Busan together and know each other better.