Emma Lee The Duchess may well mark a watershed in its leading lady Keira Knightley's career.Adapted from Amanda Foreman's acclaimed biography, it focuses on one period of Georgiana's glamorous and eventful life - her marriage to the Duke of Devonshire.

Emma Lee

The Duchess may well mark a watershed in its leading lady Keira Knightley's career.

Adapted from Amanda Foreman's acclaimed biography, it focuses on one period of Georgiana's glamorous and eventful life - her marriage to the Duke of Devonshire.

Building on what she achieved in Pride and Prejudice and Atonement, it's Knightley's most assured performance to date. Showing real maturity and emotional depth, it's easy to forget that she's still only in her early 20s.

She effortlessly captures Georgiana's complexities - the ahead-of-her-time woman who is adored by thousands, but is essentially lonely. The life and soul of the party, the impulsive, thrill-seeking gambler, the fashion icon, the sharp and intelligent political campaigner, the devoted mother, the idealistic romantic who just wants to find true love.

While much has been made of the supposed parallels with the life of Georgiana's ancestor, Diana, Princess of Wales, the Duchess's own story is so absorbing it's firmly at the back of your mind.

This may be a period film, but under Saul Dibb's direction, there's none of the misty-eyed nostalgia of a Jane Austen adaptation.

Dibb, a UEA graduate with a background in documentaries, made his cinema debut with the gritty Bullet Boy. He also directed the acclaimed TV adaptation of In The Line Of Beauty. This film really marks him out as a name to watch. Clearly a risk-taker, he boldly plays with the traditional conventions of a costume drama - it's a surprisingly pacy piece.

Some of the scenes in The Duchess are breathtaking in their nastiness.

But for all the Duke's cruelty towards Georgiana, Ralph Fiennes's performance leaves a glimmer of sympathy for him. In the hands of another actor, amid the heightened emotion, he could have easily become a boo-hiss pantomime villain. But the Suffolk actor is more subtle.

Dibb cleverly captures the Duke's personality in the locations too. Devonshire House, his London "bachelor pad" is an austere place - Georgiana has no stamp on it at all. And Holkham Hall plays it superbly.

The mismatch between Fiennes and Knightley is brilliant - for the film to work the leading players had to be a couple you would never naturally put together. And this is one such pairing. Fiennes also shows he has great comic timing. Yes, thankfully there are a few laughs to be had too - albeit the humour is quite bleak.

All the leading performances should be praised.

Hayley Atwell, who will soon also be seen in Julian Jarrold's big screen version of Brideshead Revisited, is brilliant as the inscrutable Lady Bess Foster, best friend of the Duchess and mistress of the Duke. You're left wondering what her real game plan was long after the credits have rolled.

Dominic Cooper, who this summer starred in the hit Mamma Mia, shows what a versatile actor he is, playing Georgiana's love interest Charles Grey.

It's a thoroughly gripping two hours which packs a real emotional punch. It wouldn't be surprising if there were a few nods in The Duchess's direction when awards season comes round again.