After killing his abusive father, teenage Byeong-soo (
Sul Kyung-gu) begins to believe there are people who deserve to die. As an adult he went on a killing spree and buried his victims in a bamboo grove. After killing a woman, he gets into a car accident suffers a head injury, resulting in degenerative
Alzheimer's disease. He stops killing, resumes his job as a veterinarian, and continues caring for his daughter Eun-hee (
Kim Seol-hyun). After multiple visits to the local police station (as he forgets his address), Byeong-soo strikes up a friendship with policeman Byeong-man (
Oh Dal-su). At Eun-hee's behest, Byeong-soo uses a recorder to maintain his routines. He types everything he can remember into a memoir and saves it on his laptop. Byeong-soo goes to a poetry class, where his poetic depictions of murders attracts classmate Jo Yeon-joo (
Hwang Seok-jeong). When the small town is shaken by the murders of two young women, Byeong-soo is confused and wonders if he did the killing. He goes to the bamboo grove to check for new burial sites but finds none. On the way back, Byeong-soo hits another car. Noticing a bloody bag in the other car's trunk, he collects blood on his handkerchief. The car's driver claims it is a deer's corpse and drives away without exchanging contact information. After ascertaining the blood sample is human, Byeong-soo anonymously calls the police, describing the encounter and the car's make and license plate. The tip is considered a prank as the car's driver is policeman Min Tae-joo (
Kim Nam-gil). Byeong-soo also asks Byeong-man to run the license plate separately. Instinctively realizing Tae-joo is a serial killer, Byeong-soo deduces where he was taking the body to. He finds the body and tips the police, catching Tae-joo's attention. Tae-joo goes to Byeong-soo's clinic, where he meets Eun-hee. After a short while, the two begin dating. Byeong-soo sees the pair but does not recognize Tae-joo. After Byeong-man tells him about the license plate's owner, Byeong-soo realizes Tae-joo is the killer who uses his daughter to taunt and threaten him. He gives Byeong-man the handkerchief with the blood, telling him it's from Tae-joo's car. Suppressing his self-doubts, Byeong-soo is determined to kill Tae-joo, but his failing mind and body betray him. He starts experiencing hallucinations and a week's worth of memory is erased. Byeong-soo wakes up to find himself tied up in his bedroom, with Tae-joo reading and liberally editing his memoir. Tae-joo admits to being the killer and having swapped the handkerchief with the blood sample. Byeong-soo tries to grab his bag for a weapon but fails and spills its contents onto the floor. Tae-joo threatens to kill Eun-hee unless Byeong-soo takes the blame for his crimes, then tranquilizes him. Byeong-soo wakes up and only vaguely remembers what happened. Fearing for his daughter's safety, Byeong-soo orders her to stay with his sister Maria (
Gil Hae-yeon) at her convent. He follows Tae-joo to an abandoned house and finds footage of Yeon-joo being held hostage. When he presents this evidence to the police, they suspect Byeong-soo himself is responsible. Upon trying to call Maria to prove Eun-hee's safety, Byeong-soo recalls Maria committed suicide shortly after their father's death. Police begin digging up the bamboo grove, finding the remains of past victims and Yeon-joo. At home, Byeong-soo remembers his last kill - his adulterous wife. Before dying, she spitefully said Eun-hee was not his daughter. Byeong-soo's head injury causes him to forget this revelation and he continues caring for Eun-hee. Byeong-soo recalls almost strangling Eun-hee, mistaking her for his wife, and becomes convinced that he might have killed his daughter in a fit of insanity. Guilt-ridden, Byeong-soo prepares to kill himself. However, he then hears Tae-joo confessing his crimes on the recorder, which recorded their earlier confrontation when Byeong-soo dropped his bag. Renewed with vigor, Byeong-soo calls Byeong-man and convinces him Tae-joo is the killer. Byeong-man follows Tae-joo to a remote cabin. Tae-joo strangles Byeong-man and ties up Eun-hee after she sees the body. Byeong-soo confronts Tae-joo. After a fight during which his condition almost cost him his life, with Eun-hee's help, Byeong-soo overpowers and kills Tae-joo. Eun-hee, having learned from Tae-joo earlier that her mother's body was found in the bamboo grove, is terrified of her father. He assures Eun-hee that she is not a murderer's daughter, as they are not blood-related. Byeong-soo is subsequently incarcerated and processed into an internment facility. Eun-hee listens to Byeong-soo's last recording and decides to forgive him. She visits Byeong-soo, whose memory has deteriorated to the point that he mistakes her for Maria. In a brief moment of clarity, Byeong-soo decides to kill himself before wanting to live more and remember what he is—a murderer. Before his suicide, his symptoms manifest again. Byeong-soo stands outside a train tunnel. He holds up his daughter's locket with the photo of Tae-joo inside. He sees Tae-joo smirking at him and thinks to himself, "Don't trust your memory. Min Tae-joo is still alive". == Cast ==