Billy Costigan and Colin Sullivan both enter the police force wanting to work their way up. The only thing is, Colin is really a mole, planted by Irish mob leader, Frank Costello, whereas Billy, because of his family's mob connections, is planted undercover and becomes Costello's right hand man. A first, neither man is aware of the other; Billy's point of contact is through agents Queenan and Dignam, and Colin, who works for Queenan and Dignam, has a hot line direct to Costello himself. But then it becomes clear that there is a mole on both sides of the law; will Billy and Colin be able to continue to fight for their sides without being uncovered? Or is one of them doomed to die a painful death?

I thought Leonardo DiCaprio, who plays Billy Costigan, was outstanding. DiCaprio has been much maligned by critics for his acting in the past; personally, I think if anyone has any doubts about his capabilities, then they should watch this film. Whereas I think many actors would play the role of Costigan with complete bravado, at least to the viewer's eye, DiCaprio really shows the fear and confusion that must have gone along with having such a dangerous job. At the same time, he is enough in control of his emotions to be completely convincing in his role as a mole. For me, he turned the movie from being a good thriller into being an exceptional one, he really is that good.

When I realised the Jack Nicholson was playing the Irish gangster that is Costello, I must admit I was slightly taken aback - not at the gangster bit, but rather the Irish. I think Nicholson can be many things, but convincing me that he is Irish is not one of them. Thankfully, he doesn't pretend to have an Irish accent - he may be of Irish descent, but he sounds very American. The Irish thing aside, I thought he was great. I'm not sure that it was exactly a great stretch for him to play a psychopath, but he does do it all so convincingly.

The story is very intricate and it took me a while to get to grips with it. This is not a film that you can have on in the background and still be able to follow. Having said that, the thing that confused me the most to begin with is that DiCaprio and Damon actually look quite alike, and the constant swapping between their characters just did my head in. Once I'd sorted out who was who, it was different, but that initial twenty minutes had me scratching my head a bit. Don't do what I did though and go to wikipedia for clarification - I accidentally found out how the film ended before I'd got there, which was a bit annoying.

Classification: 18