Directed by Alejandro González Iñárritu, starring Sean Penn, Naomi Watts, Benicio Del Toro, Danny Huston, Carly Nahon, Claire Pakis, Charlotte Gainsbourg, Melissa Leo, Eddie Marsan, Clea Duvall, Marc Thomas Musso and Teresa Delgado.

Visually assaulting and emotionally charged, '21 Grams' will make you sit up and rethink your own mortality.

It tells the story of remarkably intertwined existences, of people from very different backgrounds whose tragedies and reprieves draw them into each other's paths. Professor Paul Rivers (Penn) hangs between life and death, his impending demise clashing awkwardly with his wife's (Gainsbourg) desire for a child. As he awaits a heart transplant he begins to become a little more flippant with the life that he soon may no longer have.

Cristina Peck's (Watts) world may finally make sense. After years of recklessness and irresponsibility she has now found her place as a devoted wife and mother of two little girls. But the next instalment in life's plan deals her a devastating blow. Meanwhile, in a less elite part of town, ex-con Jack Jordan (Del Toro) has decided to turn to religion in the hope of redemption for earlier crimes but perhaps it is too late for him to escape the cycle that has engulfed him.

A tragic accident catapults the three into each other's alien worlds as they grapple with the enormity of what has happened to them. Through spite, hatred, revenge and gratitude, they break their former ties and embark on a journey that compels them to act instinctively, without heed for the consequences. Each one engages in a desperate bid to shake off their tag of victim, struggling to regain control over their destinies.

As they meet with unforeseen complexities, they are each forced to re-evaluate the meaning of their lives, as dependent on those around them. Their stories are for the most part bleak, delving into the gritty reality of a world that is so often tinged by sadness. But beyond the immense suffering and consuming vengeance is a story that is deeply inspirational, awakening a cascade of natural emotions.

The non-linear sequence and grainy quality of the film fittingly frame the juxtaposition of worlds apart. Penn is magnetic in the pivotal role, linking the choppy storyline through expressive narration and compassion of character. Daring to upstage him through dominance of presence is Del Toro, as the bad guy turned Christian convert who punishes himself more than life does. Completing the ensemble, Watts is assured and enigmatic in her portrayal of the emotionally challenged Cristina.

The title '21 Grams' is multi-faceted in its depth and its mystery adds wonderfully to how this film grabs you. It is tied up in life and mortality, arising out of the extraordinary detail that when death comes calling, it extracts 21 grams from the body. And the explanations for where those 21 grams go are captivating.

'21 Grams' is very much caught up in the notion of transience and wasted moments in life, but these are two hours you shouldn't mind slipping away.

Linda McGee