No attempt had been made to cover up the evidence. The clues were obvious. The name, for a start, was a dead giveaway. There's no doubting whodunit when the names on the invitation are Agatha Christie and Miss Marple. Clearly, the culprit wasn't Colonel Mustard in the drawing room with the lead pipe, but a film crew in every room in the house with a camera.

The invitation was to meet the new Miss Marple. Having acquired the rights to the Poirot and Marple stories, ITV is setting about making - or remaking in most cases - Christie's classic murder mysteries. David Suchet has long been exercising his leetle grey cells as Belgian detective Hercule Poirot. Now Miss Marple, the elderly spinster with a mind for solving crime, is being resurrected in four TV films.

Somewhere along the way Miss Marple has lost her "Miss" title. Now she's plain Marple in the title, presumably so they can use the line, DON'T MISS MARPLE in advertising the series, which begins on Sunday.

Each film has a familiar face in virtually every role. Among them are Ian Richardson, Edward Fox, Joanna Lumley, Robert Powell, Jane Asher, Derek Jacobi, Amanda Holden, Herbert Lom, David Warner, Pam Ferris, Frances Barber, Zoe Wanamaker, Elaine Paige... frankly, I could fill this page with the names.

Nice as it may be to see so many old faces, the really important piece of casting concerns Miss Marple herself. Many refuse to contemplate anyone but Joan Hickson, the BBC's choice, in the role, although Margaret Rutherford and Angela Lansbury have put on her comfy shoes as well on the big screen.

Various names, such as Prunella Scales, were bandied about when producers set about finding their new Miss Marple. Geraldine McEwan confesses she was as surprised as anyone to find herself in the running. The 72-year-old actress has a fine record in stage, film and TV, and is probably best known on the small screen for the Bafta award-winning series Oranges Are Not The Only Fruit and as the Scottish teacher in The Prime of Miss Jean Brodie.

But she made a conscious decision to avoid everything but small roles following the death of her husband, former head of Rada Hugh Crutwell, two years ago. Miss Marple came along just as she was ready to get back to work. "I really wanted to do it and when I was asked I was very, very thrilled," she says, looking smart and elegant and slightly naked without Miss Marple's large carpet bag in her hand.

"It just came at a marvellous moment. I was wanting to take on something big, something like this on film or in the theatre, so it had a rightness about it.

"It's very much the kind of thing I like doing, a character with so many different facets to her. I have grown to love her and admire her enormously as a person. I love the way she's so self-sufficient and has such interest in people, not just out of nosiness but real curiosity about human beings.

"She's an incredibly intelligent, sharp woman. She's very individual and lives totally in the present. She lives her life to the full, every moment of her existence - and I find this about her very exciting and interesting. She's non-judgemental and unshockable. That's why the other people she meets in her life like to be in her company, both young and old."

Any actress inhabiting Miss Marple faces several problems, not least overcoming the memory of Joan Hickson. McEwan knew the late actress and they once appeared in a film together. "I admired her enormously as Miss Marple. I felt a great responsibility following her but, as an actor, you can't be haunted by past performances and I'm sure audiences want a fresh look," she says.

"They don't want a carbon copy of what went before, that would be totally boring. It was the same when I did Jean Brodie on TV - Maggie Smith had done it in the theatre. We might say we'd like to see Robert De Niro play this character but would also like to see how Al Pacino does it as well. So I can't say I was haunted but totally admiring of her performance.

"I thought the combination of character was right for me. Ideally, I love to play parts that have humour but also are serious. The whole business of working out the plots intrigues me. I get a certain satisfaction out of doing it. I was very good at maths at school, doing problems and equations."

Following Hickson wasn't the only potential stumbling block. McEwan had to please both the Christie estate, which is very protective of the author's reputation, and fans of the detective stories.

McEwan is well aware of this. That hasn't stopped her and the adaptors taking a few liberties with the original, with the approval of Christie's grandson, Mathew Prichard, chairman of the company controlling her work.

The spinster sleuth's previous love life is exposed. The first film, The Body In The Library, shows her looking longingly at a framed photograph of a man in uniform. The implication is that this is her lost love, details of which will emerge in future episodes.

"She's had a relationship, possibly more than one," says McEwan. "We felt we wanted to be true to Miss Marple. I do feel that very much. I've come to admire Agatha Christie and feel very responsible to her about Miss Marple because she created a wonderful character."

She hopes the new shock ending of The Body In The Library won't upset too many fans. "It might well be considered controversial by devotees but hopefully they will keep an open mind to this being done in 2004. It's true to the spirit and essence of Agatha Christie," she says.

Miss Marple made her debut in The Murder At The Vicarage - the second of the ITV films - in 1930. She was the subject of 12 novels. McEwan didn't read all the books before filming began. "I read a couple of the novels and the short stories in which she created Miss Marple," she says. "They were written quite early on. I found with the books that Agatha Christie changes and, like Miss Marple, very much goes with the times."

Making the four feature-length films back-to-back has been hard but reunited her with many actors she's worked with or known over the years. She appeared with Ian Richardson, who appears in the opening film, with the Royal Shakespeare Company in Stratford-upon-Avon 40 years ago. She spent several years with Derek Jacobi, who appears in The Murder At The Vicarage, at the National Theatre under Laurence Olivier. And a lot of ex-students of her husband, including North-East born actress Janet McTeer, have been featured.

"For me, casting has been fantastic and a feast. I go in every day and, in scene after scene, no sooner do you finish one and there's another fabulous group of actors. Everyone says you're only as good as the people around you," she says.

Mathew Prichard has called her "the definitive Miss Marple for the new millennium". McEwan herself is happy to report she feels accepted by the Christie family. "Mathew is very appreciative and encouraging. After filming, he promised a trip to Wales to meet his mother, Agatha Christie's daughter. It's a family thing and I feel as though I've joined the family," she says.

* Agatha Christie: Marple - The Body In The Library is on ITV1 tomorrow at 9pm.