Sean Penn has made a film of Jon Krakauer's book "Into the Wild," the story of Christopher McCandless, a young man who throws over - throws apart, really - everything that was laid out for him: Harvard Law School, money, a suburban life - and sets out for his dream. The dream is Alaska - not the Alaska of today but Jack London's wilderness, where he will live and survive until - well, until he dies. Which he does. End of story.

The more important question is why, and in an effort to answer the question Krakauer and Penn have pieced together the fragments of Christopher's life in the two years before he got to Alaska. First he gives his remaining college fund to Oxfam. Then he sets out west from Georgia, where he grew up. He doesn't tell his parents (William Hurt and Marcia Gay Harden in thankless roles) or his sister and never writes or phones them. He loses his car in a flash flood, then carefully removes the plates so he won't be identified. We follow his odyssey as he hitches, rides the rails, gets to the Pacific and meets up with longtime travelers Brian Dierker and Catherine Keener; rafts through part of the Grand Canyon, then up to South Dakota where he meets a rowdy farmer (Vince Vaughn), then down to the Imperial Valley where he spends time with an aging widower, Hal Holbrook.

Everywhere he goes he's adopted, cared for, taught good skills, welcomed into his hosts' lives, but always moves on toward his dream. As played by Emile Hirsch he's like a big puppy to them all; I think they see him as the part of themselves that never got to live out their own dreams, though they all seem happy enough as they are.

He calls himself Alexander Supertramp, and his dream is so obviously suicidal that it's odd no one's called him on it, but the people he finds are themselves self-imposed outcasts from society.

And then he gets to Alaska, where he's dropped off at a trailhead, slogs along till he finds an abandoned bus and makes that his headquarters; he's found his dream, in the Thoreauvian quote: "Rather than love, than money, than fame, give me truth." Umm, okay, but as anyone with half a brain, and certainly anyone who has a degree from Auburn, as he does, could tell him, what is truth? That question never comes up in the film.

And that for me is the frustrating thing about "Into the Wild," and about Christopher McCandless, and Sean Penn's screenplay and film; there's never any insight into Christopher; in fact Penn implies that he, maybe like Christ, brings joy into the hearts of his friends. In any case he exists outside of any frame of reference I might know. We're told, in a narration by his sister Carine (Jena Malone) that their father was a brutal man and a bigamist, who fathered another boy after Christopher was born; both children were bastards. Obviously it's crucial to understanding Christopher, and Carine for that matter, but Penn lets it just sit unexplored.

Penn's cinematographer is Eric Gautier, the man who photographed that beautiful film "The Motorcycle Diaries;" but I think Penn's own editing is needlessly choppy, and he's reluctant to let his scenes play out in their own rhythm; he cuts from person to person in that old-fashioned Hollywood studio style. And another caveat: I think he's chosen the wrong music for the film; there are a lot of Eddie Vedder songs where I at least would have preferred the more authentic Woody Guthrie or Aaron Copland. Nevertheless there are moments of great beauty here, and Penn's achievement is to let us see them.