Inspector Ma Yue-lung (Lawrence Cheng) bumps into his ex-classmate and longtime lover, Julia (Rosamund Kwan), while catching a thief.

They both later go to an alumni reunion and see another ex-classmate, Ma Yau-yau (Tony Leung Ka-fai), who is now Julia's superior.

Heavy Crime Bureau chief Pau Yu Chat (Kenneth Tsang) sends Lung to go undercover to take Yau's job.

Later, Julia brings Lung to meet a land developer, Tang Kwok-kiu (Damian Lau).

Another inspector, Shek Chun (Waise Lee), then gathers evidence and is determined to bring Tang to justice.