Byeong-soo, a retired serial killer, lives a quiet life with his daughter Eun-hee, who has cared for him ever since his Alzheimer’s diagnosis. When Eun-hee brings home her new boyfriend Tae-joo, Byeong-soo realizes Tae-joo is also a serial killer. To save his daughter, Byeong-sop must fight Tae-joo as well as his own mind.