"Remember this, if you see someone doing something but at the same time watching you... then he is a cop"
Triad boss Hon Sam (Eric Tsang) sends a group of young gangsters to join the Hong Kong Police academy with the hope that they will infiltrate the department, rise through the ranks and help him to avoid the attentions of the Police. One of the most successful of these youngsters is Lau (Andy Lau) who ascends the chain of command rapidly. One of Lau’s fellow cadets Chan Wing-yan (Tony Leung) is expelled from the Academy but secretly becomes an undercover cop, hoping to infiltrate Sam’s Triads.
The film is full of suspense and suspicion as we go back and forth between the two moles, both trying to discover the other’s identity while keeping theirs hidden. The plot is highly original, complex and fascinating but it’s a shame I’d already seen Martin Scorsese's fantastic remake The Departed because I knew how things were going to pan out. Even though I knew the ending there were still enough differences and surprises to keep the action fresh. The film also feels much more like a Michael Mann film than a Scorsese.