More compelling than the story told by director Alejandro González Iñárritu in ‘‘21 Grams’’ is the brash, non-linear manner in which he tells it.

Iñárritu — rapidly emerging as Mexico's pre-eminent filmmaker (it's either him or Alfonso Cuaron of ‘‘Y Tu Mamá También’’) — is no novice when it comes to audacious narrative techniques. He also directed the sinuous urban saga ‘‘Amores Perros’’ (2000), which some critics (wrongly, I think) compared favorably to ‘‘Pulp Fiction.’’

Iñárritu's latest effort, which derives its title from the amount of weight that the human body supposedly loses at the moment of death, is actually more ambitious and rewarding than ‘‘Amores Perros.’’ Like a stranger's photo album, it tells a story obliquely, but profoundly.

Making his English-language feature debut, Iñárritu — who also directed the BMW-sponsored short film ‘‘The Hire: Powder Keg’’ — drops us into a chopped salad of images and scenarios involving three troubled but otherwise unrelated people. Paul (Sean Penn, in a performance that rivals his work in ‘‘Mystic River’’) is a terminally ill math professor whose wife (Charlotte Gainsbourg) wants to conceive while he awaits a donor heart. Jack (Benicio Del Toro) is a born-again ex-con whose strident devotion to Jesus often burbles over into anger and violence. Lastly, there's Christina (Naomi Watts of ‘‘Mulholland Drive’’), a one-time drug addict who has built a content, rewarding upper-middle-class life with her husband and two small daughters.

With nothing to indicate whether these images of addiction, sickness and recovery reside in the past or present, we're not initially sure if these people are moving toward or away from ruin. What we do know, from the very beginning, is that something horrible eventually conspires to put them in a hotel room together, battered and frantic, with life pumping out of Paul as quickly as his blood can carry it. Slowly, rivetingly, the sad mysteries iron themselves out.

With no disrespect to her co-stars, Watts owns this movie. Confronted by a tragedy almost too horrible to ponder, Christina is thrown into utter emotional chaos, and I have never seen an actress so wrenchingly surrender to a scene. The dialogue, by ‘‘Amores Perros’’ scripter Guillermo Arriaga, is jagged and unflinching and remarkably tight for a writer not working in his native tongue.

‘‘21 Grams’’ is not a perfect movie. Paul, a nicotine addict who continues to smoke after his operation, seems to crave his own quick demise and we're never sure why — though anti-smoking advocates will be pleased with the unflattering depiction of tobacco use. Moreover, Iñárritu struggles to maintain the experimental tempo of the first part of the movie down the final stretch, a failing that also thwarted ‘‘Amores Perros.’’ It's a testament to his raw talent as storyteller — and ability to generate indelible images — that he keeps us engaged even after the pace flattens out.

IF YOU GO

‘21 Grams’
Starring: Sean Penn, Naomi Watts, Benecio Del Toro
Playing: Opens Friday exclusively at Camelview in Scottsdale
Rating: R (profanity, sexuality, some violence, drug use)
Running time: 2 hours, 5 minutes
Grade: A-