Overview: Detective Investigation Files IV (Chinese: 刑事偵緝檔案IV) is the 4th and final installment of the Detective Investigation Files TV franchised by TVB in Hong Kong. It is a complete reboot of the series, with new cast. The series focuses on the lives of two detectives, Tsui Fei (Louis Koo) and Kong Chi Shan (Sunny Chan), and the murder cases they deal with.