The narrator did it. Roger Ackroyd was murdered by Dr James Sheppard, the very man who tells us about his death. He only admits to his crime in the final chapter, claiming that the whole account leading up to the revelation as “the history of one of [Hercule] Poirot’s failures”. But as with the best Christie mysteries, the clues are there all along, hidden in plain sight.

One screams out: Ackroyd is murdered over the contents of a letter that fingers Sheppard for a previous crime. Ackroyd receives this letter in Sheppard’s presence and starts to read it aloud – before going mysteriously quiet and saying he wants to finish it alone. “The letter had been brought in at 20 minutes to nine,” Sheppard tell us. “It was just 10 minutes to nine when I left him, the letter still unread. I hesitated with my hand on the door handle, looking back and wondering if there was anything I had left undone.”

Clearly not, as we learn later. That’s the most outrageous moment in the book and easy to miss among all the initial excitement. After that, the signs are there – but far more subtle. I particularly enjoyed the report of a vital telephone call made to Sheppard shortly after the murder was committed. Here’s what he tells us after he picks up the receiver:

“What,” I said. “What? Certainly I’ll come at once.”

I ran upstairs, caught up my bag and stuffed a few extra dressings into it.

“Parker telephoning,” I shouted to Caroline, “from Fernly. They’ve just found Roger Ackroyd murdered.”

You’d have to be smart to realise first time around how significant it is that Sheppard only gives us his side of the conversation. He isn’t lying, but he is hiding the truth. Many similarly elegant sleights of hand allow Christie to prevent us from feeling cheated when we eventually realise Sheppard’s guilt, and also to keep us in suspense. I read it almost 100 years after publication (and just one week after reading Endless Night, which has a very similar plot structure), yet it still felt sharp.

The book has consistently impressed critics, too: in 1926, the New York Times labelled it a “superior mystery”, while the Observer said it made “breathless reading from first to the unexpected last”. More recently, in 2013, the Crime Writers’ Association voted it the best crime novel ever written. Even so, Laura Thompson’s introduction to the current UK paperback refers to a “myth” that critics didn’t like it, and that the trick ending annoyed the public.

Endearingly, TS Eliot seems to have loved Christie. I’ve been unable to find any Eliot reviews of Roger Ackroyd, but there is a Criterion article published in 1927 in which he outlines his ideals for a good detective story. Mainly, he says they should follow the laws of his favourite, The Moonstone. They are splendid:

(1) The story must not rely upon elaborate and incredible disguises.

(2) The character and motives of the criminal should be normal. In the ideal detective story we should feel that we have a sporting chance to solve the mystery ourselves; if the criminal is highly abnormal an irrational element is introduced which offends us.

(3) The story must not rely either upon occult phenomena, or, what comes to the same thing, upon mysterious and preposterous discoveries made by lonely scientists.

(4) Elaborate and bizarre machinery is an irrelevance.

(5) The detective should be highly intelligent but not superhuman. We should be able to follow his inferences and almost, but not quite, make them with him.

On point five, with those sleights of hand, Christie excels. She also passes most of the others with flying colours. But on point four: the time of the murder is central to the plot and Sheppard sows confusion by having a Dictaphone play a recording of Ackroyd’s voice after he has killed him. A 1920s Dictaphone might not quite have been a “bizarre machine” but it does feel like a flimsy device to support such an elaborate plot. Would it have sounded real enough to fool someone on the other side of a locked door? Meanwhile there’s only one reference to the machine before it becomes so crucial to the plot, when the butler tells Poirot that Ackroyd didn’t buy one. Is that fair? And we are expected to believe further confusing guff about Poirot realising the machine must have been in place because of the way a chair had been moved to conceal it?

Oh well. These problems don’t seem to have bothered Eliot too much: he was still recommending the book to friends as late as 1955. Nor has it unduly troubled generations of contented readers. Christie may have outwitted us, but we don’t feel unduly cheated.