Bo-na, Tae-sung, and their four-year-old daughter Yul are a typical happy and harmonious family. After a three-year parental leave, Bo-na returns to work and successfully completes her duties from day one, defying concerns. Meanwhile, Tae-sung, covering a drug case, learns a serial killer who disappeared four years ago has returned.

Tae-sung and the police are surprised by Kingfisher's return and resolve to finally apprehend Kingfisher for good this time. Tae-sung seeks information from Detective Dong-jin, who previously pursued Kingfisher. Meanwhile, a new employee appears at Bo-na's company, seemingly harboring an unknown secret.