Music student Yeon-seo receives disturbing news that something bizarre has happened to her sister. She hurried to Seoul to meet her sister, but there, she was surrounded by the police and many strangers. Police said her sister had committed suicide and sealed the case. However, Yanshu always felt that there was more inside story, so she decided to uncover the truth by herself
At the same time, the famous detective Kim heard about this and became very interested in this case, so he decided to re-investigate. Yeon-seo and Kim start to investigate together, gradually uncovering heartbreaking and shocking clues.
At first, they just wanted to find out what caused Yanshu's sister to commit suicide, but soon they discovered that behind this seemingly simple suicide incident, there was a more complicated and terrifying truth hidden.
During the investigation, they found some clues that someone seemed to be deliberately covering up the truth. Someone tried to keep this seemingly suicide case unknown, and Yeon-seo and Kim's investigation drew obstacles and threats from some uninvited guests.