Kwon Yeon-woo is a somewhat naive 30-year-old low-level civil servant who works in a city hall branch office. After moving into a new apartment, he encounters a high school girl, Soo-young, and sees her on his way to work every morning. She is a cheerful and eccentric 18-year-old who lives with her mother downstairs from him. Over time, the two begin to develop feelings for one another.