Not many actresses get a career-changing chance at 68.

For Julia McKenzie, already a successful stage and TV performer, it came when she was chosen as British television's new Miss Marple, Agatha Christie's famous amateur detective.

The new series, to be broadcast on the commercial ITV channel from September 6, has already been shown in the United States, Canada and Ireland, underlining the international appeal of one of Christie's best-loved creations.

At home, though, critical attention is likely to be at its most intense, with McKenzie seeking to fill the shoes of previous popular interpreters like Margaret Rutherford, Joan Hickson and, most recently, Geraldine McEwan.

It's the prize, McKenzie said of her high-profile role.

And to come at this time in my career, which normally is tailing off, she said in a recent interview. I would have retired, I think, because I don't want to end up saying 'The carriage awaits'.

It's a funny thing about acting, you know, when you get the part and you're my age, you drop 10 years like that. Acting makes you feel young again.

McKenzie learned she had got the part while on holiday in New Zealand.

My legs emptied, McKenzie recalled. It was really a hell of a shock, and what was even more of a shock was that I had another week to go.

They flew out scripts to me ... and I was on camera 10 days later, it was that quick. Maybe it was a blessing, maybe I didn't have time to think about it.

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McKenzie said she was trying to bring something new to the part after McEwan's tenure.

When Christie picked up the character 10 years later it was a tweedier, sturdier person, and obviously I'm not going to do a pale imitation of Geraldine so I went for the other one.

Her first appearance is in A Pocket Full of Rye, a story written in 1953 in which Rex Fortescue is found poisoned and the only clue to his murder is a pocketful of rye. The police are perplexed, as it seems everyone has a motive to kill him.

The actress best known for television series Fresh Fields and Cranford said she was committed to 16 episodes in all.

Miss Marple's appeal, she believes, is partly down to nostalgia people feel for the 1950s, when we were all nicer to each other, had a bit of respect for each other, and partly because each story turns the viewer into a detective.

The fact the character travels so well may lie in the fact that Marple is quintessentially a quaint old Brit, she added.

In Britain, television audiences for previous series reached up to 10 million, according to estimates, and Christie is a global publishing phenomenon.

Christie's official website says she is the best-selling female author in the world with two billion books sold, and is second only to William Shakespeare and the Bible.

I didn't realize her (Marple's) appeal was so international, just everywhere, McKenzie said.

That's very scary, because people have their own image of Marple. It's hard for them to accept another physical being.

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