A serial killer with heightened hearing kills people using his ability. For this reason, Kang Kwon-Joo (Lee Ha-Na), who also possesses this ability, is caught off guard. Kang Kwon-Joo suffers from post-traumatic stress disorder following the death of Do Kang-Woo, but continues to carry out her duties as a supervisor at the 112 emergency call centre. This time, Kang Kwon-Joo teams up with Detective Derek Jo (Song Seung-Heon) to catch the serial killer. Derek Jo is a strict man who tolerates no mistakes. He is the head of the LAPD (Los Angeles Police Department) unit dealing with criminal gangs.