What becomes of a movie star when the career hits a hiccup and the lustre starts to fade? If the movie star is smart, they go back to basics, reconnecting with the fire of their formative years. What drove them back then? What first made them strive for greatness? "When I was a kid I always wanted to kill Hitler," Tom Cruise revealed recently. "I hated that guy and all he stood for."

Valkyrie, then, is not just the latest Tom Cruise action thriller. It is the fruition of a dream; a boyhood fantasy writ large; a Hollywood blockbuster that provides an opportunity that was denied him in life. Inevitably he bungles it.

Bryan Singer's picture casts Cruise as Claus von Stauffenberg, the Wehrmacht colonel who spearheaded the 20 July 1944 plot to save the fatherland. Wounded in battle and sporting a natty eye-patch, von Stauffenberg has grown sick of war. He wants to "show the world that not all Germans are like Hitler". He hates that guy and all he stands for.

The obvious sticking point here is that (spoiler!) von Stauffenberg did not actually kill Hitler. The plot failed and the conspirators were executed. Played as a tragedy, or a stark study of failed ambitions, this might not have been a problem. Except that Singer opts to frame Valkyrie as a high-concept wartime suspense thriller, inviting us to suspend our disbelief and go along for the ride.

The 1944 plot was at least fiendishly planned and generally well executed. Singer's, by contrast, seems flawed and foolhardy from the start.

But what of Singer's co-conspirator? Valkyrie paints von Stauffenberg as the archetypal "good German", a model of elegant disenchantment. And yet Cruise, for all his skills as a performer, does not do disenchantment. For all the anguished moments of doubt, the constant stares into the mirror, his von Stauffenberg is essentially Top Gun with an eye-patch.

The film's curious melange of dialects only underscores this quality. Von Stauffenberg's cohorts are played by British actors (Bill Nighy, Terence Stamp, Kenneth Branagh) who deliver their lines in English accents. The villainous Nazi is portrayed by German actor Thomas Kretschmann who speaks English in a German accent. And then - standing separate and apart - is Cruise himself, intoning his lines in pureblood American. He might as well have been dropped in from an Allied plane; a gung-ho Hollywood hero sent in to clean up a very European mess. He couldn't manage it as a kid, and he can't quite do it now. Hitler one; Tom Cruise nil.