The ancient, wrinkled lady curtseying with arthritic caution before the Queen seems almost too perfectly cast in the role of the gentlewoman mystery writer. And why not? Agatha Christie has been turning out full-length whodunits—83 of them at last count—since 1920, and at 84 years of age is firmly established as the Mistress of the Macabre. She is the most published writer in history; hundreds of millions of copies of her books have been sold. Her play The Mousetrap is enjoying its 22nd year, the longest run in British stage history. And now the smash success of the film adaptation of her Murder on the Orient Express—which was honored recently by a royal command performance—only serves to introduce a new generation of crime buffs to Dame Agatha.

For all her fans, Christie's discreet reclusiveness makes her a conundrum even the intuitive Miss Marple, her favorite fictional detective, would despair of cracking. On an income of between five and ten thousand dollars a week, the author moves among two stately manor homes and a town house in London she shares with her second husband of 44 years, Sir Max Mallowan, a distinguished archeologist. The two old parties still motor down to London periodically, to shop, see friends and go to the theater, or dine in one of Max's very correct clubs.

The plots still come easily, if sometimes in a bizarre fashion; she once gained inspiration for a mystery by soaking and munching in the tub so long she lined its rim with apple cores. It's the writing that drags. "Nobody ever really enjoys work, do they?" she says. Currently, she presents her grateful publishers with finished manuscripts at a rate of about one a year, always delivering in time to have a new Christie in the bookstalls by Christmas.

How do her old books hold up? Well, she says, lots better than the movies that were made from them. While admitting to liking the new Orient Express and the 1958 classic, Witness for the Prosecution, she frankly loathes the MGM version of her Miss Marple. "Margaret Rutherford was a very good actress," she sniffs, "but she was nothing like my character. Every single one of those [films] was awful."