Just when you thought Sean Penn had the Best Actor Oscar locked up for his career high in Mystic River, along comes tough competition: himself. In this scorcher of a drama from Mexican director Alejandro Gonzalez Inarritu -- it's only his second film, after the brilliant Amores Perros, and his first in English -- Penn burns with ferocity and feeling as Paul, a math professor faced with the possibility of death after a heart transplant. His wife (Charlotte Gainsbourg) wants to have a baby, something of him left behind. Paul sees spirituality in terms of numbers, the twenty-one grams (the weight of a hummingbird, a chocolate bar or a stack of five nickels) that leave our bodies at death. Is it the weight of the soul?
Clearly, Inarritu and screenwriter Guillermo Arriaga aren't afraid of tackling big issues or splintering a plot -- as they did in Amores Perros -- to make audiences work at putting the pieces together. They intensify the puzzle by adding two equally damaged characters. Cristina (Naomi Watts), an ex-junkie, is the widow of the man whose heart Paul carries. Jack (Benicio Del Toro), the cause of the heart donor's death, is an ex-con Jesus freak and alcoholic who loves and menaces his two kids and his wife (Melissa Leo, in a staggering portrayal of conflicted devotion). How these characters -- all kicked hard by fate -- unite in a brutal, erotic and achingly tender dance of death is for the film to tell you, not a review.

But know this: You won't see more explosive acting this year. Penn's continuing mastery of his craft amazes. Del Toro gets so far inside this ruined hulk that you flinch; he's astonishing. And Watts is miraculous in an all-stops-out performance that bleeds with anger, guilt, sexual hunger and incalculable loss. That Inarritu shapes something redemptive out of blasted lives is proof that he is a filmmaker of rare and startling grace.