I had already heard about this film a few years ago. I knew it was a Chinese gangster film, that was about it. I prefer old Chinese films, i.e. films that deal with the days when disputes were settled with fists and swords. Those were the good old days, and it has to be said that the Chinese films in that genre, especially those made since the reunification with Hong Kong, have been outstanding. I find modern day Japanese gangster films dull, so I was never tempted to watch "Infernal Affairs", assuming it would be similar in style. I was very, very wrong.
This is a psychological drama, a cat and mouse game in which it's uncertain who is the cat and who is the mouse. Chan Wing is a police officer who is planted as an undercover operative in a gang. Lau Kin is a gang member who has infiltrated the police force. Years pass by. After 10 years Chan Wing has become the gang boss's right hand man, while Lau Kin has become a senior police officer. After a drug trafficking operation goes wrong both sides learn they have a mole. Because of their trusted positions both Chan and Lau are above suspicion, and they are each assigned the duty of finding the mole. Moles, I should say. The gang boss asks Chan to find the mole in his gang, while the police want him to get information from his boss who the mole in the police force is. On the other hand, Lau is put into the internal affairs department and told to find the mole in the police force, while the gang boss is telling him to find the mole in the gang. If that sounds complicated, it is. Things come to a head when the two men finally meet one another.