Paul (Sean Penn) is a gravely ill professor awaiting a heart transplant; early on, we see him in his bathroom, carefully removing his respirator and smoking a forbidden cigarette. Cristina (Naomi Watts) is a recovering addict who adores her husband and young daughters; Jack (Benicio Del Toro) an ex-con trying to re-establish himself with his family and faith. These people live in the same anonymous city, but have no connection, moving in different worlds — until a tragic accident brings them together.
Like "Amores Perros," the previous collaboration of director Alejandro González Iñárritu and screenwriter Guillermo Arriaga, "21 Grams" tells three separate stories; more so than the previous movie, it twists and whips the stories together, creating a seemingly random timeline that's challenging to follow. The story starts in the middle, wanders back to the beginning, and eventually makes its way to an end. It's disorienting to watch, and some will question whether the convoluted storytelling adds to or takes away from the drama. Like some of the characters, the audience is without an anchor; we spend much of the movie sorting out just what's going on — we've got a soulful puzzle to process, just as Iñárritu's three tragic heroes do.
Shot with a hand-held camera by Rodrigo Prieto (cinematographer for "Amores Perros"), the characters are literally shown in shades of gray; all have dark, hollow smudges under their eyes. And under this harsh, bleached-out spotlight, the actors deliver beautiful work. Penn, in particular, has a quiet nobility to him; he looks much older than he did in "Mystic River," and his thin face has a gravitas to it, his eyes pained and yet gentle.
The title of "21 Grams" refers to the weight the body loses at the time of death. It's a lyrical image — the weight of the soul? The emotional weight shifted to those we leave behind? In the end, as snowflakes fall softly on a shabby motel pool, Iñárritu manages to leave us hopeful; he's shown us his character's souls, in all their raw beauty.