There are two ways you can make screen biographies. You can tell the truth and, at least in America, risk getting sued. Or you can doll up a life like a kindly preacher at a funeral.

But Steven Shainberg, who came to attention with Secretary, which dared to present us with a sado-masochistic relationship which was highly satisfactory for both parties, has found a third way.

In Fur, he presents us with a fairy tale about Diane Arbus, controversial photographer of the Sixties, that doesn't pretend to represent the facts. He merely wants to suggest how this once conventional wife and mother might have become the legend she was.

Nicole Kidman plays her and that alone should draw an audience over and above the fact that the Arbus portraiture, grim and possibly exploitative as it often was, changed the whole tone of still photography.

We see her, in a prim Fifties dress, assisting her fashion and advertising photographer husband (Ty Burrell) who shoots conventional photos for her rich and bullying father's Fifth Avenue fur and department store. That much is true.

The rest is pure fiction as she discovers a man in the room upstairs who is peculiar, to say the least. He is an ex-circus performer who is so covered in hair that he resembles Cocteau's Beast. And she, of course, is the beauty.

Fascinated by the man, who is clearly fascinated by her, Arbus spends more and more time with him. She watches as his circus friends gather in his apartment, each some sort of freakish mutation from the normal. And she learns to love rather than fear them.

It is fortunate that Robert Downey Jr has wonderfully expressive eyes, because that's about all we see of him as the hairy man upstairs. It makes acting difficult but not impossible and Downey does what he can with his soulful sockets.

Kidman, however, is better served. She shows us how an ordinary woman becomes unordinary through the experience, though we never see her work that caused such a furore at the time, and does so even now.

What we do see is her husband's increasing pain as he realises she might be drifting away from him. So he grows a beard and hopes for the best.

Shainberg's film is long and slow, in contrast to Secretary, and nothing like as powerful in making its point. What's more, it tells us less about Arbus than we want to know. But at least it is attempting something audaciously different and Kidman's performance keeps it alive.