On a raining evening, middle-school student Yeo-Seon (Kim Sae-Ron), resident of a middle-class apartment complex, walks home alone from the bus stop, but she doesn't make it home. 10 days later, her decapitated body is found in a red suitcase. Gyung-Hee (Kim Yunjin) is Yeo-Seon's stepmother. She carries tremendous guilt, because she did not pick her up stepdaughter on the evening that she was abducted. A few days later, Gyung-Hee is so startled, she falls to the floor in the parking lot of her apartment complex. A girl stands in front of her. The young girl's name is Soo-Yeo (Kim Sae-Ron) and she carries an uncanny resemblance to her murdered stepdaughter. Soo-Yeo also lives in the same apartment complex. Another 10 days later, the murderer has yet to be caught and he has killed again....