At the same time Marisa Hagen (Jacinda Barrett) discovers that her child (Tom Russell) is seriously ill, she also finds out that her husband (Richard Roxburgh) has been unfaithful for years. Marisa goes on a bizarre search in an attempt to turn her husband’s serial affairs into a positive – an illegitimate child could save her son’s life. A chance encounter with another parent, Connor (James Nesbitt) and his son Finn (Kodi Smit-McPhee), leads them on an unpredictable journey of love and hope.

A strong and honest melodrama about real people.

Matching Jack has a squirmy kind of emotional truth to it. It’s funny, but it’s not a comedy. It has graphic and harrowing scenes where young kids, cancer sufferers, must endure the awful symptoms of a terrible disease; or else undergo painful and invasive medical procedures. And there’s a melodramatic plot line that keeps the movie’s energy on high when its basic premise could be enough to sink it into an abyss of trite TV movie of the week heartache. It’s also got a large dose of whimsy, and jarring scenes of domestic upset. And people cry a lot and often. This is one busy movie.

Still, director Nadia Tass makes sense of all this mess. Working from a script by David Parker (who produced and shot it) and Lynne Renew, Matching Jack plays honest and strong, mostly because the characters seem less like writer’s constructs and more like real people – bewildered, and often belittled in their suffering and embarrassed and angry by their own desperation when faced with death.

The movie is built around Jacinda Barrett’s Marissa, 30-something mother of only child Jack (Tom Russell). This is a good thing; Barrett’s character is really tortured by the script, but it’s a performance rich in detail and nuance, where it easily could have degenerated into a tearjerker’s version of a scream queen.

When Jack is diagnosed with leukaemia Marissa is dealt a double blow; she discovers that her architect husband David (a splendidly restrained Richard Roxburgh) is a serial philanderer who has decided to leave her for Veronica (Yvonne Strahovski), who is pregnant with his child.

Told by their physician (Colin Friels) that Jack’s best chance of survival is a bone marrow transplant from a sibling, Marissa starts researching David’s extremely long list of flings (which seem to stretch back nearly two decades). Meanwhile, David has to face up to his own commitments.

Marissa’s door-knock adventures – confronting David’s ex-lovers – are sometimes funny, sometimes wince-inducing. As a metaphor for mother love it’s pretty strong; it’s Marissa’s struggle to subordinate her ego in deference to her son’s suffering that keeps the movie alive.

But then the plot offers Marissa a bit of an escape clause, too; she falls for an eccentric Irishman, Connor (the great James Nesbitt), whose son Finn (Kodi Smit-McPhee) has befriended Jack.

There’s a lot more plot, too, and some it is surprising. What’s interesting about the tone of the film, which is essentially very sweet, is that Tass and co. work very hard at conveying the rigours and hardships of cancer sufferers and the subtle culture of an oncology ward – with its special language and 'codes’. (There’s one particularly poignant bit of plot business about the fact that every kid destined to die ends up with a free Playstation 3.)

Shot on a short schedule, there’s nothing spectacular about Tass's technique or Parker’s widescreen photography; it’s earthy and straightforward.