“The Debt,” directed by John Madden (“Shakespeare in Love”), is the perfect cinematic example of a “mixed bag.” At one moment, it’s complex, nuanced and thrilling. At the next, it’s dumb, shallow and implausible. These switches occur often and without warning, making for a film of such inconsistent quality that I don’t know whether to recommend it or urge you to stay away.

The story, adapted from a 2007 Israeli thriller, documents the lives of three retired Mossad secret agents (Helen Mirren, Tom Wilkinson and Ciarán Hinds) who have been praised for decades following their completion of a mission to take down an infamous Nazi (portrayed by the frightening Jesper Christensen). Flashbacks (featuring Jessica Chastain, Marton Csokas and Sam Worthington) to the time of their assignment, however, reveal that a few key details have been altered for the public eye.

Madden adeptly alternates between the present-day scenes, set in 1997, and the 1960s flashbacks. The shifts feel natural and, more importantly, both timeframes contain compelling stories. It also helps that the film’s characters are in the hands of actors with skill beyond anything this movie deserves.

The younger trio, anchored by Chastain’s charisma and grace, is consistently appealing and admirably overcome one of the most ill-conceived love triangles I’ve seen in a while. Mirren and Wilkinson, meanwhile, lend class to the film and provide predictably competent performances. I’ve heard complaints that the older actors don’t resemble their younger counterparts in demeanor or appearance. This didn’t especially bother me, but in the hands of lesser actors, it might have.

More unfortunate is the decision to equip each actor with a Hebrew accent, to varying degrees of failure. Worthington, in particular, can’t shake his Australian twang. This is, apparently, meant to trick the audience into thinking that the actors are actually speaking Hebrew. All it really did was give me a headache.

Speaking of headaches, the love triangle I mentioned is sure to cause a few. In theory, I have nothing against a good love triangle, especially when each member is portrayed by an actor as likable as the ones in “The Debt.” The screenwriters are to blame for this particular failure.

We’re informed from the beginning that the main characters are hardened Israeli spies. What we’re shown instead are three erratic, emotional, easily manipulated agents who act as if a real-life romance is part of their mission. This would be fine if it were done in a fun, cheeky manor. It’s not. I promise you, “The Debt” is anything but fun. The climax involves two senior citizens writhing around on the floor stabbing each other. Not fun.

For the most part, though, the plot held my interest due to the moral questions at hand—for years, the characters have agonized over a very controversial decision. The film should encourage some thoughtful debate, despite its plot holes and annoyingly simplistic ending. I should also note that cinematographer Ben Davis uses the story’s diverse locales to great effect and the action sequences are executed nicely.

“The Debt” is too self-serious to overcome its many flaws, but I won’t deny the appeal of spending two hours with Helen Mirren, Jessica Chastain and Tom Wilkinson. Madden’s film doesn’t waste their talent, but it certainly isn’t worthy of it.

Grade: C+