Falsely accused of murder, Na Ok-min is arrested. In the next cell, Suh Pil-sun sits, his eyes focused on the ceiling. He has an old booklet and a necklace with a strange pattern. He gazes at Ok-min. Ok-min's mother is murdered. Pil-sun dies in prison. Pil-sun's old booklet and necklace have been placed at the head of Ok-min's bed. Afterwards, Ok-min is found not guilty and released from jail. Those involved in the murder of Ok-min's mother are killed off one by one. Suspecting that Ok-min is the serial killer, the investigators look into every detail. They realize that the murders occur when Ok-min is asleep. It is revealed that Ok-min's spirit had been killing those responsible for her mother's death.