If there is a lesson to be taken home from Martin Scorsese’s new movie, it must be that Irish gangsters are more ruthless and bloodthirsty than Italian gangsters. This is a dark and gritty crime thriller that clearly draws some of its inspiration from recent Boston police scandals. If the premise didn’t warn us that this is going to end with bodies stacked like cordwood, the name of the director should be a tip-off.

This might make an unpleasant film but it is saved (at least for me) by the charisma of the actors. Rarely do we get to see such talented performers having so much fun portraying really evil people.

Most charismatic of all is Jack Nicholson as Frank Costello, a mob boss who makes Tony Soprano look like a wimp. You won’t find this guy visiting a psychiatrist; he has not a trace of neurosis. He is a happy, well-adjusted mass murderer who really likes himself. (However it is never made clear why a man who can’t say three sentences without reminding us how Irish he is has the same name as a famous Italian gangster.)

Matt Damon plays Detective Colin Sullivan of the Massachusetts State Police. A bright charming golden boy who has risen rapidly through the force, he is actually a mole working for Costello.

His arch-enemy, though he doesn’t know it, is Billy Costigan (Leonardo DiCaprio), a deep-undercover agent sent to infiltrate Costello’s gang. This is a great scenery-chewing role that is probably a cinch to earn an Oscar nomination.

The lives of the two intertwine in various ways while they play a cat-and-mouse game trying to identify and unmask each other, as each pretends to be working for the other side. Sullivan always seems smug and confident while Costigan seems to be in a state of perpetual terror. Soon Costigan is seeking counseling from a pretty psychiatrist (Vera Farmiga) while Sullivan, unknowingly meeting the same psychiatrist, charms and romances her. This is just one of those movies where the bad guys have all the mojo.

The plot descends through a series of overlapping betrayals to the inevitable bloody conclusion. The whole thing manages to be quite entertaining, though far from uplifting.