A serial killer with an enhanced hearing ability appears. The serial killer murders people using his enhanced ability. Because of this, Kang Kwon Joo, who also has an enhanced hearing ability, is driven into a corner. Kang Kwon Joo cooperates with Detective Derek Jo to catch the serial killer. Derek Jo is a person of principal, who doesn't allow mistakes. He is a team leader from the LAPD. His LAPD team dealt with criminal gangs.

Meanwhile Kang Kwon Joo has suffered from PTSD since the death of Do Kang Woo, but she still carries out her duties as the the leader of the emergency 112 call center.

It's following the lives of 112 emergency call center and dispatch team as they fight against an international evil cartel involved in the internet's dark web.

Kang Kwon Joo, now a National Director of 112 Call Center Division, brings her main team from HQ to Poongsan city to investigate the death of their Dispatch team's leader there. She meets and then appointed Do Kang Woo, a lone and hot-headed detective with mysterious past, as their new team leader.