Atonement; Starring: Keira Knightley, James McAvoy, Romola Garai, Saoirse Ronan, Brenda Blethyn, Harriet Walter, Gina McKee, Vanessa Redgrave; Dir: Joe Wright; Cert: 15; 2hrs 5mQuite simply, this is one of the most extraordinary films you will see this year - or perhaps for the next three or four years.

By Andrew Clarke

Atonement; Starring: Keira Knightley, James McAvoy, Romola Garai, Saoirse Ronan, Brenda Blethyn, Harriet Walter, Gina McKee, Vanessa Redgrave; Dir: Joe Wright; Cert: 15; 2hrs 5m

Quite simply, this is one of the most extraordinary films you will see this year - or perhaps for the next three or four years. It's a breath-taking piece of original film-making which has brought, what many said was an unfilmable book, safely and satisfyingly to the big screen.

It's a film that is impossible categorise. It's a romance, it's a period drama, it's a literary adaptation, it's a war film, it's a mainstream movie and it's a surreal art house movie all in one. It's all these conflicting elements wrapped up as a cinema-going bundle and then defined by an extraordinary clever screenplay by Dangerous Liaisons writer Christopher Hampton and some beautiful and brilliantly unconventional camerawork by young Pride and Prejudice director Joe Wright.

It's a film that needs to be seen on the big screen; not only for the gorgeous photography and marvellous soundtrack, which has sounds start as sound effects and then carry-on as part of the musical score, but because it is a film which is deliberately slow to get going and audiences may need to be restrained from using the remote control to fast forward some sections of the first 20 minutes.

The film builds steadily from the slow beginning into a gripping and sensational denouement and you need the detail and the information from the beginning to get the full impact of the story.

It's a film which is not easy to discuss on the page because not everything you see on screen is intended to be real. Events are played out and then revisited and retold later from a different characters point of view and you do not know which version is correct until the end of the movie.

It's a film about class, about relationships and how jealousies, misunderstandings and not having the courage to do the right thing can ruin people's lives.

The film opens in a country house in 1935. Keira Knightley plays Cecilia, a privileged young socialite recently graduated from Cambridge and looking for a rich husband. Her younger sister Bryony, played at first by Saoirse Ronan and then Romola Garai, is smitten with Robbie (James McAvoy) the well-spoken gardeners son who has been sponsored through university by Cecilia and Bryony's unseen and conspicuously absent father. Now he wants to train to be a doctor.

But there is a underlying sexual tension which threatens to destroy their idyllic summer - Robbie loves Cecilia and Cecilia loves Robbie but neither can acknowledge this as they bicker and squabble on the lawn. The problem is exacerbated by the fact that Bryony also has a crush on Robbie and when she spies Robbie and Cecilia making love in the library, she accuses him of molesting a cousin in the grounds.

Robbie, not being from the aristocracy, is immediately imprisoned while Cecilia turns her back on her family. The story then jumps forward four years to 1940. Robbie is out of prison and serving in France, Cecilia is a nurse while Bryony journeys to London to atone for the great wrong she has done.

It's a compelling story driven forward by the rhythmic sound of a typewriter on the soundtrack which acts as a bizarre storytelling metronome. Director Joe Wright draws out some startling performances from Keira Knightley, who has never been better on screen, and allows McAvoy to give the kind and gentle Robbie a tremendous sense of dignity.

The story is largely told from Bryony's point of view except when she has no direct view of the scene in progress. The tour-de-force moment in the film is a stunning five minute, one take stead cam shot of the beach at Dunkirk prior to the evacuation where Wright's restless camera follows Robbie and his comrades across the packed sand dunes, past a number of horses being put down, past a stranded Thames barge, onto the promenade, through the crowds, onto a bandstand, then past an abandoned fun-fair, before heading back along the prom in front of a collection of army vehicles having their radiator grills smashed and onto a café/bar on a nearby pier where Robbie decends down into a basement cinema where he is finally dwarfed and framed by a French love scene being played out in an empty room.

It is a surreal moment which would not have been out of place in Richard Attenborough's Oh What A Lovely War.

A brilliant and unconventional film, which deserves to win every major award going. An extraordinary achievement and not quickly forgotten.