“I don’t have an opinion,” says the hero of Fifty Dead Men Walking, a tightly wound based-on-a-true-story set in the violent final throes of The Troubles.  

“You’re Irish,” replies his mother. “You were born with a fookin’ opinion.”

Alas, the motivations of Martin McGartland (Jim Sturgess), an opportunistic young Belfast hustler-turned–IRA informant, are brought into focus over the course of Kari Skogland’s movie. It’s just tough to discern what’s running through the heads of the many other operatives and cops who blur the screen. IRA men are either bloodthirsty thugs or misty-eyed freedom fighters, the lawmen are noble peacemakers or Imperialist lackeys, and the MI5… well, they’re stabbing everyone in the back. Fifty Dead Men Walking is a film that thrives on ambivalence but gets bogged in the very confusion it’s trying so artfully to convey.

Blame for this could be deflected onto the dialogue coach, who, to Canadian ears anyway, plants West Belfast so firmly in the mouths of the largely non-Irish actors that Skogland practically revels in the bonus layer of impenetrability. The cast fends for itself remarkably well: Sturgess and Ben Kingsley, working the subtle end of his gift for submersion as McGartland’s British police handler, form a palpable — if thinly explained — bond as two men whose convictions and confidence wither amid the conflicts. Natalie Press and Canadian Kevin Zegers go well beyond the girlfriend/best pal routine and deepen the script’s rather rote supply of loyalty tests. (Only Rose McGowan flubs it as a deadly Provo militant: one of the few main players with actual Irish parentage, her accent gets lost somewhere between Derry and Mumbai.)

This is a problematic movie about a problematic topic — not just The Troubles themselves, but an autobiographical source whose author is either a hero (the title refers to the lives McGartland believes he saved by informing) or a traitor. Fifty Dead Men Walking walks the fence and trips. Sturgess, Kingsley and co. win the extra star.