Although Miss Marple had a long literary career, with her first novel published in 1930 and her last, Sleeping Murder, in 1976, in total, excluding short stories, this only ran to 12 books. There seems to be several reasons for this, partly because her publishers seemed to prefer Hercule Poirot and also because Christie sometimes found difficultly in creating a plausible scenario where Miss Marple could be integrated into the action.
After her debut appearance in 1930, Miss Marple didn't appear in another novel until 1942, with only one more appearance that decade. The 1950's and 1960's were her most prolific period however, with four novels in the 1950's and three in the 1960's.
One reason why she may have started to appear more regularly during this time is that Christie herself was now Miss Marple's age, and possibly Christie could indulge herself a little by voicing some of her own thoughts and opinions through her character.
This certainly seems to be the case in At Bertram's Hotel, where we find Miss Marple staying at the luxurious London Hotel. Although it's the 1960's, visitors could be forgiven for thinking that they've stepped back in time sixty years. This allows Miss Marple to muse about some of the drawbacks of modern life and compare how things were when she was a girl. Everything at Bertram's seems a little too good to be true, and so it probably is. And what connects the hotel to a major train robbery?
Published in 1965, At Bertram's Hotel is very much towards the end of Agatha Christie's career. Generally a good rule of thumb is to be cautious about any of her books published after the late 1950's. They are not all bad, by any means, but there's no doubt that she lost her fine edge of plotting and the whodunnits are generally less convincing.
This BBC4 full cast dramatisation starring June Whitfield is able tweak the source material slightly to produce a story that flows well, but there's no denying that the train robbery subplot never really integrates into the Bertram's story, and the eventual explanation for the disappearance of Canon Pennyfather seems unlikely to say the least.
But a talented cast of actors help to cover some of cracks in the material, and it makes for a diverting couple of hours entertainment.