Se-jin, a young woman who lives in an old apartment in a Seoul suburb, amuses herself by observing the windows of the apartments on the other side. One day, she notices that the lights of some of these apartments are turned off at the very same time. She begins to suspect that this pattern is somehow related to a series of mysterious deaths in the neighborhood. She becomes more and more deeply involved as she attempts to solve the mystery.
Thirty-year-old Yun-woo bumps into a high school student in the elevator while on his way to work. His heart starts pounding at this teenager’s boldness. At a subway station, KANG Sook can’t stop staring at the long-haired, beautiful Ha-kyung. Ha-kyung breaks up with KANG Sook only a few hours after they first meet. However, KANG Sook has already fallen in love with her.