Sung-soo, who is a successful businessman, lives with a wife and child in a luxury apartment. One day, Sung-soo received an call informed that his brother was missing, so he came to his brother's house to search for him. There, Sung-soo saw many strange symbols carved on the door, and met Joo-hee - his sister. Joo-hee said that someone was watching them, and they were in danger.