In the world of 21 Grams, no life happens without death, and no death happens without life. Blame and guilt flow from one person to another as easily as their fluids and organs are transfused and transplanted. Although the numerous parallels would seem to give the movie balance, equal parts joy and despair, in the doomed thermodynamics of 21 Grams, an external force tugs down hard on everything, a great equalizer that sucks the middle class wife of an architect into seedy motel rooms and pulls grime out of the pores of math teachers and ex-cons alike.

The story follows three lines: a woman whose husband and children are hit by a car and killed, the criminal trying to go straight who is driving that car, and the man who receives the heart of the dead husband. The movie doesn't follow any one of these lines linearly. For the first half hour, the episodes spill out in a seemingly random order, presented as a tease, asking us to guess whether the beard or the clean-shaven face came first, the wife or the girlfriend, the blood or the hospital, the prison or the church. Director Alejandro González Iñárritu showed an affinity for twisted timelines in his debut feature, Amores Perros, but here he has taken it up a notch.

The question, of course, is what does he say by telling us the story in this manner. The three story lines have similar and related themes of loss — loss of family, life, and faith — but the non-linear narrative seems unnecessary to highlight that fact. All of the losses stem from the same event, so no fancy temporal shifts are needed to make them coincide. Maybe Iñárritu wanted to reflect the lives of his characters in his editing structure, and indeed their lives do seem to go in loops. A character who receives a heart transplant finds out that his body isn't accepting it and he'll need another one. A man who has turned to Jesus to try to stay clean begins to think Jesus is leading him back to jail. And an upstanding mother of two with cocaine in her past turns to her old dealer when her life falls apart. For these people, the order of events hardly seems important, so why should the order of the scenes in the movie?

Even so, it's hard to shake the impression established early on that Iñárritu is playing a game that overtakes his characters. After its initial jerkiness, the movie does settle down for most of its mid-section into a linear tale with brief forward flashes, but the game isn't over. Gradually, the characters become pawns. They're no longer acting according to logic or emotion but instead according to the filmmakers' desire for an ingenious structure, a hall of mirrors. People do things in order to appear appropriately ironic. The living kill, the dying give life, the fatalists find purpose, the guilty do their time, face death, turn out to have been framed, and then beat the rap with what can only be described as ironic benevolence from their creator. No image is complete until it has been reflected in at least two surfaces; a man remembers the eyes of the girl he killed not just when he looks in a mirror, but when he looks in the mirror while making love.

That we feel anything at all for these characters whose lives are chopped into slivers says that something here works. Much of the credit goes to the three lead actors, Sean Penn, Naomi Watts, and Benicio Del Toro, but the actors in the smaller parts are just as good. And the underlying emotions — grief, revenge, and the feeling of being predestined to suffer — seem real and complexly intertwined, so real that one wonders if the filmmakers found them too raw to depict head-on.

Iñárritu withholds the answers to a few mysteries until the end, both large ones (where did all that blood come from?) and small ones (what made the woman laugh when she left the pool?), but by then, like the final pointless moments of a long lost chess match, whose finger is on the trigger and whose fluid is in whom hardly matters.