Former serial killer Byung Soo gets diagnosed with Alzheimer's. The doctor tells him that it's due to the aftereffects from a traffic accident 17 years ago; the same accident that stopped him from his killings and allowed him to live a normal life with his dear daughter. So when a series of murders occur near his town, Byung Soo gets worried whether the killings are his doing during his memory lapses. But then he comes across Tae Ju and instinctively realizes that he is the serial killer. He reports this to the police, only to learn that Tae Joo is one. Byung Soo tries to find firm evidence that Tae Ju is a psychopath, but only raises Tae Ju's interest in him and his daughter. And now with his memory slipping, Byung Soo must find a way to protect his daughter from Tae Ju. Adapted from the bestselling fiction book by author Kim Young Ha.