Choi Youngjae is a police officer at Seoul Metropolitan Police Agency. He has stacks of paperworks and he can’t afford to take any other cases, but when one of his best friend and fellow officer was murdered drastically by a single cold gunshot, he doesn’t mind taking a few more cases.

The interrogation with the suspect was suppose to go smoothly, but the moment he stepped into the room, something was wrong. The suspect wasn’t scared, he was laughing. The suspect proceeds to tell Youngjae that it wasn’t him.

This time.

He continues to tell Youngjae disturbing details only the police knows of cold cases going back from years ago. What gets even more weird is, peculiarly the recording device, shows up blank, as if there wasn’t any conversation from the start. Of course, everything Youngjae has to report is dismissed— it’s complete nonsense, nothing can be proven and someone is just trying to mess with his mind, right? Then, why does he feel like he’s being watched by someone everywhere he goes, as if waiting for him to make a move?

Youngjae was determined to unravel the murder of his best man, so he decided to make this his last and final case. With the help of Kim Juhyun, a female criminal profiler, they uncover secrets that could possibly have answers to a cold case that shook the entire nation.