How can an actress from England who doesn’t appeal to me at all in interviews as her very British self — how can she so mesmerize me as a Canadian shiksa goddess of marital perfection in the film “Barney’s Version”?

Only an exceptional actress could ever pull that off.

Unadulterated goodness is, I feel, the hardest and most challenging thing for any actor or actress to play. No one really believes you can be that sainted, least of all yourself.

Having worked with a few of the female greats, Katherine Hepburn and Meryl Streep, and met a few others such as Bette Davis, I found the unadulterated health and blistering sanity of Rosamund Pike’s Miriam in “Barney’s Version” most astounding.

Everyone in the audience just has to fall in love with her during our first glimpse of this vision of her Miriam’s low key, Canadian nobility.

We actually drop off a cliff in the same way alcoholic, eternally Boychick Barney does. She is, of course, strikingly beautiful but eloquently frank and irresistibly unselfconscious. How does Barney win her and keep her for as long as he does? That is the major flaw in the script.

Barney is not who he appears to be, based, as I’ve learned, on the original novel’s author, the renowned Canadian writer Mordecai Richler. Barney has received none of the world’s weighty homage as Richler has. Barney is a successful producer of lightweight television fare. Rosamund Pike’s Miriam was not only not born yesterday but is insightfully generous in her first encounter with Barney and every appearance following that.

Perhaps Mr. Richler’s startling humility may well have inspired Barney’s disturbingly flawed humanity. It is perhaps the novelist’s self-image by comparison to his perfect wife, the very woman Pike says she based her performance on. However, we find it hard to believe not Pike and her performance but the screenplay’s story-telling.

However, Pike’s commitment to the script itself and the powerful simplicity of her performance carries you along through the arduous and nakedly revealing saga of Barney Panofsky and his oddly matched, third and longest marriage. You believe she actually feels fated to marry, live with and endure Boychick Barney.

Ultimately “Barney’s Version” is a wonderfully challenging journey for anyone to experience and, in the end, quite remarkable for the feelings it evokes. Paul Giamatti plays Barney Panofsky with the same abandon he performed America’s firey John Adams with. His refusal to pander for audience sympathy takes us on a much richer adventure than I, for one, was prepared for.

I don’t think I’ve ever experienced a film quite like it. Why?

Rarely is a whole man shown to us in almost any story-telling format, whether novel, theater or film. Our knowledge of Barney in the end is almost embarrassingly complete. We are a bit shocked that we could come to know another human being that well in so short a time. Thanks to Richler’s selfless honesty and Giamatti’s courage, we do.

With the oft-repeated question, “What is she doing with a guy like that?” hammering at us so frequently, we constantly doubt the credibility of this intensely realistic, beautifully performed and impressively directed film.

By a very odd and left-field way of comparison, the musical “Nine,” based on Federico Fellini’s very autobiographical “8 1/2,” carries no suspension of disbelief, not only because of its form and style as a musical, but the errant ways and seeming insanities of not a decent but a great film director. His foibles are almost de rigeur. What else could you expect from genius?

But Barney as a genius?!

Barney’s greatest achievement in life was finding and marrying Miriam. That is, in turn, Mordecai Richler’s selfless homage to his own wife.

That timeless gift to Mrs. Richler almost absolves whatever drunken excesses the author might have wandered into as a Barney, rendering them and the film a surprisingly Catholic confession with the audience as priest.

Of course we forgive him. He’s not only Barney. He’s Mordecai Richler!