Sarah (Winslet) is in a bit of state. She doesn't get on with her toddler daughter and she's discovered her dullard husband worships at the altar of an internet porn queen.

While she's made to feel inadequate by the coterie of privileged mums at the school-gates, she also resents their stiflingly conventional lives and petty prejudices.

When "prom king" Brad (Wilson), a chiselled stay-at-home dad, arrives in a local swing-park, Sarah feels attracted and mischievously engineers a kiss in front of the incredulous moms.

It turns out that Brad is one-time college football star who can't quite make into law school and is overshadowed by his controlling documentary-maker wife (Connelly).

The impish prank in the park soom blossoms into a fully-fledged affair as Sarah and Brad attempt to escape their empty, emotionally barren lives with lung-busting trysts in her attic room.

OK, so far this is a routine plotline worn thin through oversuse yet director Todd Field lends it a bitterly sardonic spin with the introduction of another character - Ronnie (Jackie Earle Haley).

He's a convicted sex offender - the perceived paedophile bogeyman of every parents' nightmares - who lives with his mother and is the subject of bitter campaign of persecution by Brad's football pal Larry (Noah Emmerich).

Ronnie's arrival profoundly alters the dynamics of this self-congratulatory suburban society - his mere presence soon whips up a maelstrom of distrust that will inevitably end in heartache.

Field perfectly illustrates this when Ronnie takes a dip at a pool frequented by mums and their kids and it empties with a rapidity reminiscent of the shark scare scene in Spielberg's Jaws.

Every character is subtly drawn and given an emotional depth which results in their actions ringing with authenticity. Even Ronnie is shown to be only too well aware of his urges but unable to banish them.

It's a beautifully textured, graceful movie which credits its audience with the intelligence to make up their own minds courtesy of a delicately ambiguous ending.

Tim Evans