Moo Jin Hyeok, a police detective, finds out that his wife was killed while he was working. The police then catch a suspect and he is put on trial. However, Kang Kwon Joo, an officer from the emergency call center, testifies that that man is not the killer. She states that he sounds different from the voice she heard while on the phone with the victim. She then asks the court to listen to the recorded call, however, the voice of the killer is not heard on the record. She also, states that the killer is the same person who killed her father. In the end, the suspect is freed because of her. A few years later, Kwon Joo becomes the emergency call center chief at the station Jin Hyeok works at. He is furious after knowing that and goes to confront her. However, she gets a call from a kidnapped girl and orders Jin Hyeok to go look for her before she is killed.