On the eve of her sixteenth birthday Mila's family decided to explain to her the reasons behind her adoption, now four years later she finally has enough money saved to live independently of her wealthy adoptive parents.

Mila starts her quest to discover her roots in Seoul, the city she was born in. But will she find more than she bargained for whilst searching for herself? Mila is a cynical girl and when she by chance meets a guy who claims to not want anything romantic from her, she is suspicious. But when he reveals her is also willing to help her with her plans of exploring Korea, she is hard-pressed to turn down his offer of friendship. She's not one for believing in fate, no matter how much her new friend is and when she starts to notice herself caring again, Mila realises she's gained much more than friendship from her visit to her homeland. 

Kim Jongin is a young, successful star. Considered to be charming and exotic, he knows he's perfect. But when he notices a strange girl leave her notebook behind on a train he stumbles into terriotory he wasn't sure really existed. Train Girl doesn't fall for him at first sight, or first text, and that makes her interesting. Determined to get to know her better, Jongin hatches a plan so that he can spend time with her. Only to find all his efforts are foiled by his other members, and his attempts at keeping train girl a secret are far from successful.