Anonymous Signal

After joining the police force, Kwok Pak-fei (Joel Chan), Keung Hey-man (Moon Lau) and Lau Lik (Jazz Lam) look up to their mentor Law Yau-bong. The quartet have developed a close relationship. Rewind three years, and Yau-bong is killed in the line of duty in a manhunt. And Lau Lik is seriously hurt. Hey-man blames Pak-fei for the tragedy as he is eager for quick success. Their friendship is broken. A serial murder case again brings Pak-fei and Hey-man together. Undercover officer Wan Ka-lei (Tiffany Lau) is instructed to infiltrate a crime syndicate. However, she runs into her ex-boyfriend Chiu Chun-long (Owen Cheung), and they get entangled.