Eun Chae-ni is the granddaughter of a wealthy restaurant owner. She is smart, polite, and diligent in everything she does, but because she has a different heart from others, she becomes more stubborn as she grows up, and she lives her life on thin ice that may stop at any time, dreaming of a train trip. Lee Woon-jung is a mysterious civil servant with many secrets and no social skills. He is a lonely person who can hardly be by anyone's side, but he comes to realize the meaning of 'us' after meeting Eun Chae-ni.