Tom Cruise, his reputation defamed, his career desperately in need of a makeover, has chosen as his comeback vehicle a film in which he plays a Nazi officer who tries to kill Hitler. C’mon, Tom, you’re not making this easy on us. Couldn’t you have gone with a story that would allow your character to, oh, I don’t know, succeed?

“Valkyrie” is the film, nimbly directed by Bryan Singer (“X-Men”) and based on a true story about an elaborate, complicated, almost-successful assassination attempt that occurred in 1944. Cruise plays Nazi Col. Claus von Stauffenberg, who at the film’s outset has already been sent to the North African front as punishment for his outspokenness against Hitler (although he must not have been too outspoken, since he’s still alive). He’s one of a growing number of officers who believe that, as he puts it, “We can serve Germany or the Fuhrer, but not both.” Germany is losing the war under Hitler’s direction; the only hope is to remove him from power, cut their losses, and make peace with the Allies.

Once Stauffenberg’s opinions become known throughout the underground, he’s brought into the inner circle of coup plotters, whose numbers include a lot of high-ranking German officers — a lot more than you’d think a cabal could have and still remain secret. Unfortunately, with their similar uniforms, their matching British accents, and their near-universal middle-aged-white-maleness, it’s hard to keep track of them all in the film, but they’re led by Major-Gen. von Tresckow (Kenneth Branagh) and Gen. Beck (Terence Stamp), now retired from duty but still keenly interested in the future of Germany. Gen. Olbricht (Bill Nighy) is onboard but overly cautious; Gen. Fellgibel (Eddie Izzard) is a communications officer whose cooperation will be vital; and Gen. Fromm (Tom Wilkinson) — by far the most interesting of the lot — manages to endorse the plot without doing so openly, thus remaining sufficiently two-faced to save his own neck.

More participants are involved than I have named, played by less famous actors and given less screen time; the film, feeling obligated to remain true to life, introduces more characters than it knows what to do with. It even presents von Stauffenberg’s wife, Nina (Carice van Houten), only to whisk her away again before she has a chance to add anything to the story.

This shadowy group’s plan involves planting a bomb in Hitler’s bunker, killing him, then quickly gaining control of the government by misapplying a back-up plan called Valkyrie, which Hitler designed to be employed in the event of civil unrest following a catastrophic Allied attack. It’s actually a rather brilliant scheme to use the government’s own strength against itself — and it would have worked, too, if it hadn’t been for you meddling kids!

Written by frequent Singer collaborator Christopher McQuarrie (“The Usual Suspects”) and Nathan Alexander, “Valkyrie” is gutsy for telling a story that we know won’t end well, and admirable for telling it in a way that’s occasionally suspenseful. Like all good espionage dramas, it’s full of furtive glances, knowing looks, and hiss-whispered conversations, and that’s moderately enjoyable as far as it goes.

What it’s lacking is a human element. The still-charismatic Cruise and the others give adequate performances, but there’s just too much plot, and too many characters to contend with, for it to hit home with us. Furthermore, it rarely rises to the level of entertainment you expect from a wartime thriller — there’s something rote and foregone about the whole affair. The only real thrill is in discovering how, exactly, the assassination attempt will fail, and what terrible consequences it will lead to for the perpetrators. The destination doesn’t need to be happy, but the film ought to make the journey more lively than this.

C+ (2 hrs.; PG-13, some violence.)