What happens when the party years fade and the fullness of life starts to sour? That's the central question posed in this drama about a junkie, rock star's wife trying to accept the responsibilities of adulthood on her own terms.

Tragedy is the catalyst, although it's clear things are going downhill fast when we first meet Emily (Maggie Cheung from In The Mood For Love and star of Assayas's earlier Irma Vep) and fading Brit rock star husband Lee (James Johnston) before he performs a gig in a grungey club in Canada's industrial hinterland.

Lee's career is nose-diving. He's the first to admit his latest album is dire. Lee's close friends and associates, even the music press, seem to think the shrill, aggressive Emily is to blame for wrecking his life and career. After a fight, the two go their separate ways for the night: Emily drives to a desolate suburban spot overlooking the local oil refinery, shoots up, and slips into unconsciousness. Meanwhile, Lee ODs in their dingy motel bedroom.

With a six month jail sentence, a methadone programme, no career, no money and no friends, Emily is scraping along the bottom. Aimless. Lost.

Emily slowly realises that she must pull herself together, not just for herself, but also for her estranged young son, who lives with Lee's parents Albrecht (Nick Nolte) and Rosemary (Martha Henry) in the West Coast city of Vancouver, Canada.

Nick Nolte puts in a magnificent performance as the grizzled, sage father-in-law who gets a second chance at fatherhood with both his grandson and his daughter-in-law. In danger of sounding banal, it's a film about a divided family learning to support each other after a tragedy. Assayas pays attention to the mundane details of Lee's death, funeral arrangements, how the bills are paid and how Emily can support herself. Dull reality seems constantly snapping at Emily's heels ready to pull her into the humdrum of daily existence.

But there is no danger of the film being banal. It flits from Canada, to Paris, to London, hovering around the fringes of the rock scene. Beatrice Dalle (Betty Blue) appears as an old friend of Emily from the music world in scenes in Paris and there's a cameo appearances from alt rock star Tricky (you only see him sing, not speak). There's cool tunes too from minimalist Brian Eno. The story leads in multiple directions, until eventually Emily's own aimlessness begins to dissipate and it finds a rhythm.

Olivier Assayas's mercurial directing will also keep you on your toes. More than most directors Assayas's direction revolves around and amplifies his characters' emotional wellbeing. At first, in the club, there's a long groovy scene of the band playing with lots of handheld work, throbbing music, vivid lighting that captures the excitement of being at the gig. Emily's nighttime drug scene at the refinery has a bleak beauty. When she goes looking for work from an music industry friend in Paris, the shiny, media offices with their space station frigidity reflect Emily's growing sense of alienation from that world since her husband's death. And so on.

When we are with Nolte - who we first meet by an old sailing boat on a sunny beach - scenes are bathed in warm light and comforting. Nolte seems such a huge presence on the screen alongside the confused and desperate Emily.

Maggie Cheung, who is married to Assayas, does well to keep you interested in what is, at least initially, a highly unsympathetic character, as she is put through the emotional wringer. Credit, too, to the director too who moulds his film so subtly and effectively around the central character.