All actors are taught to put on the skin of their characters over their own; some do it better than others, and along with Sean Penn and Meryl Streep we can add Don Cheadle to that amazing group. Think of his work in "Hotel Rwanda," as the manager of a hotel in Kigali, balancing his own life and family along with that of a thousand refugees. Think of "Talk to Me," the underrated and barely seen film about a charismatic, jailhouse DJ who becomes a wonderfully witty commentator and radio personality in Washington, D.C., who can't quite handle the acclaim and then self-destructs.

Now, in a film from an idea by Steve Martin (yes, that one), he plays Samir Horn, a Muslim man with a Sudanese father and an American mother, who apparently is a member of a terrorist organization aimed at the United States, both here and in a number of locations around the world. We meet him as he's showing some other terrorists how one builds a bomb. He's arrested in Yemen and put in jail with another committed man, Omar (a wonderful performance by the French actor Said Taghmaoui). The organization stages a prison break and the two men end up in Marseille, where Samir and his group plan another bomb attack, this time on the American consulate in Nice.

He is being tracked by an American FBI agent named Roy Clayton, played by the perfectly cast Guy Pearce, wearing last year's mustache, goatee and suit, and who is a wonderfully inventive and resourceful opponent of Samir. I won't take you any farther into the plot of the film, because here is where "Traitor" exposes its fatal weakness: can we really believe that Don Cheadle is actually going to play a committed anti-American terrorist? Of course, the answer is no. And so everything that happens in the film simply postpones the revelation that he is, in fact, a deeply embedded U.S. agent whose mission is to find the head of the terrorist group.

That in itself wouldn't be bad, if the film then shifted to a suspenseful chess match between Samir and that man, but it doesn't quite, and the climax of "Traitor" is just too bizarre to believe. It's a shame, because director Jeffrey Nachmanoff has taken his time with each episode, unlike, say, the frantic pace of the last two Jason Bourne features, which in a way this film resembles. Nachmanoff has the camera study his people, examine them at leisure, and lets his scenes play out in real time. And yet nothing he does will change the fact that we simply cannot believe that Don Cheadle, as good as he is, is a traitor. If the film were made in another country, with actors unknown to us, it would be easier to buy into its premise; but its power is undone by its casting.