As soon as Jack's gang boss utters the line "I don't want to be a product of my environment...I want my environment to be a product of me..." you know you're onto something.

In fact, you're onto Martin Scorsese's best movie in an age, one that sees him returning to the terror firma of the gangster epic in the style of Goodfellas. And it's the one that finally bagged him that elusive Best Director Oscar.

Nicholson is the big draw as Irish mobster Frank Costello, a ruthless urban dictator whose steel will is enforced by a vicious band of trusted lieutenants.

One invisible presence in this cut-throat corps is Matt Damon's Colin Sullivan, a Massachussetts State Police Force hotshot who passes every shred of useful intelligence back to Frank.

Frustrated by their inability to take the teflon-coated transgressor down, Boston's finest arrange to daringly place a mole deep undercover in Frank's racketeering ranks.

He's Billy Costigan (DiCaprio), a rookie cop who grew up in dodgy South Boston and has family mob links that make him the ideal informer.

And so it goes. Billy grasses Frank up to his rozzer colleagues while Colin feeds Frank information that allows him to stay one step ahead of the law.

Until, that is, both cops and crimmos realise there's a traitor in their midst and set about discovering who the rat is.

This is rich and satisfying stuff with Scorsese rediscovering his masterful skill at delivering a narrative which crackles with acid dialogue delivered by a gifted cast.

Damon is coolly callous as the department's dark star while DiCaprio delivers the director his best performance yet as the edgy, jittery mole constantly on the brink of being rumbled.

That's not forgetting Mark Wahlberg (surprisingly the film's only acting Oscar nominee), who nearly steals the show as a snarling, sewer-mouthed sergeant and Costigan's point of contact within the force.

It's gritty going - fonts of rhesus negative redecorate walls while Frank's novel method of testing Costigan - his broken arm gets the boot - makes the eyes water.

Based on the red-hot Hong Kong thriller Infernal Affairs, Scorsese sticks to the plot but gives it a gritty Irish Catholic spin, even leaving room for a dig at the church's recent paedophile problems.

Even a final reel which sees the violence accelerating to a rough marriage of the closing credits of the Benny Hill Show and the St Valentine's Day Massacre can't spoil the show.

It's good to see Marty remarried to the mob.

Tim Evans