Synopsis

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. Pak-fei and Hey-man keep receiving mysterious messages, so their boss sets up Mysterious Message Intelligence Unit by merging the two teams of officers. They look into bewildering murder cases. Why the hints sent by some phone assistant can always guide the team to solve cases ahead of time? Is "she" a friend or a foe?