She wrote to her great-nephew, David West, combining Christmas wishes with an urgent request for information.

Fortunately she was invited, as on previous years, to the vicarage for Christmas dinner, and here she was able to tackle young Leonard, home for the Christmas season, about maps.

Maps of all kinds were Leonard's passion. The reason for the old lady's inquiry about a large-scale map of a particular area did not rouse his curiosity.

He discoursed on maps generally with fluency, and wrote down for her exactly what would suit her purpose best. In fact, he did better. He actually found that he had such a map amongst his collection and be lent it to her. Miss Marple promising to take great care of it and return it in due course.

"Maps," said his mother, Griselda, who still, although she had a grown-up son, looked strangely young and blooming to be inhabiting the shabby old vicarage.

"What does she want with maps? I mean, what does she want them for?"

"I don't know," said young Leonard, "I don't think she said exactly."

"I wonder now…" said Griselda. "It seems very fishy to me… At her age the old pet ought to give up that sort of thing."

Leonard asked what sort of thing, and Griselda said elusively:

"Oh, poking her nose into things. Why maps, I wonder?"

In due course Miss Marple received a letter from her great-nephew David West.

It ran affectionately:

"Dear Aunt Jane

Now, what are you up to? I've got the information you wanted. There are only two trains that can possibly apply – the 4:33 and the 5 o'clock. The former is a slow train and stops at Haling Broadway, Barwell Heath, Brackhampton and then stations to Market Basing. The 5 o'clock is the Welsh express for Cardiff , Newport and Swansea . The former might be overtaken somewhere by the 4:50, although it is due in Brackhampton five minutes earlier and the latter passes the 4:50 just before Brackhampton.