In the year of our Lord 1932 the first thirteen Miss Marple stories were collected into a book, The Thirteen Problems. The 1953 edition of this book contained a forward by Agatha Christie in which she said that Miss Marple is better suited to short stories (unlike Poirot, who does better with novels). I find this quite interesting:
I enjoyed writing the Miss Marple stories very much, conceived a great affection for my fluffy old lady, and hoped that she might be a success. She was. After the first six stories had appeared, six more were requested, Miss Marple had definitely come to stay.
She has appeared now in several books and also in a play—and actually rivals Hercule Poirot in popularity. I get about an equal number of letters, one lot saying: “I wish you would always have Miss Marple and not Poirot,” and the other “I wish you would have Poirot and not Miss Marple.” I myself incline to her side. I think, that she is at her best in the solving of short problems; they suit her more intimate style. Poirot, on the other hand, insists on a full-length book to display his talents.
These Thirteen Problems contain, I consider, the real essence of Miss Marple for those who like her.
This may contain something of an explanation for why Miss Marple is so little in her own books. She is more in them than she is in her short stories—she’s often only in a page or so of the short story—but the belief that she is better at solving short problems may shape the novels so that other people do the long work and it is presented to her as only as a summary, such that for her it is a short problem.
I can also see what Agatha Christie has in mind. Miss Marple does a little investigating in A Caribbean Murder and most of the investigating in Nemesis, and as much as I liked both I have to admit that it didn’t quite feel right. People should come to her, rather than the other way around. In some sense I think that the essence of Miss Marple is not precisely that she is intimate, but that she is domestic. This relates to how Sir Henry Clithering would always tease Miss Marple about how the people in a crime remind her of people from the village; the whole point is that the public world was not really larger than the domestic world. When Miss Marple does the investigating, she ventures outside of the domestic sphere. It is right, in a sense, for someone else to do the investigating in the public world then bring it to her, where she uses her knowledge of the domestic world to solve the problems of the public world.
That said, the way she does the investigation in Nemesis does not violate this; one of the parts of the domestic world is visiting other domiciles. Old ladies visit each other, and pay calls, and chat about local and family things, and Miss Marple mostly solves the mystery in Nemesis using these tools.
All that said, of the short stories and novels, I’m inclined to say that The Body in the Library was the best of the Miss Marple stories. So I suppose I must respectfully disagree with Dame Agatha, though I will say I think that she’s right when she said that the Thirteen Problems contain the essence of Miss Marple. They give you a clear sense of who and what Miss Marple is, but I do not think that they are her at her best.