Yeon-hee, a righteous police officer, struggled with a working mother and raised her son Doyeon alone. Do-yeon, who is 20 years old, grew up to be a 'normal child' with a good heart like her mother's wish. But the dark shadows of serial killings begin to fall on the lives of two happy people. Will Yeon-hee welcome "it" as a mother, who is tightening herself and her son? Will he fight back with the police?