As somebody who loves Agatha Christie's novels, and loves adaptations of her books, I am an avid defender of the ITV adaptation of Miss Marple. Both Geraldine McEwan and Julia McKenzie are superb in their own interpretations of the character, meaning that every episode is a pure delight to watch. The Secret of Chimneys is definitely among the best of the episodes!
Having watched this the very afternoon of finishing the book, it is worth mentioning - as all other reviews do so temperately - that they have strayed from the book. Very far. To the point of being completely unrecognisable. Fair enough - this particular book is a bit of a nightmare to adapt - but one does wonder why they didn't just...adapt a different story? Although this TV series is famous for changing plots rather radically, this was the first time I saw a book completely rewritten almost without a trace.
HOWEVER, I don't care about novelistic accuracy. In fact, I admire the way that the 'Agatha Christie's Marple' series changes the plots. If the film is good in its own right, that is all that matters! A film is an entirely different thing, and the film is not the book. For example, several reviewers slate the Marple adaptation of "The Sittaford Mystery" for too many deviations. Whilst I myself do not like that film, my dislike has nothing to do with the inaccuracies: my dislike stems from it just not being a particularly well-directed film.
The Secret of Chimneys though, as a film in its own right, is fantastic! Beautiful production values, well-shot, classic Christie (everyone up at a country house...) and, as always, an absolute standout performance from Julia McKenzie as Miss Marple. She has earned my full respect with her work on the role; she is flawless.
Bravo!