Mrs Ferrars lay dead, presumably by her own hand. Roger Ackroyd, who had been in love with her, knew she was being blackmailed but she would never name the person who had her at their mercy. But after she died, a letter arrived for Ackroyd in her hand – a letter that would finally reveal her secret.

But it seems the blackmailer was also aware of the letter, and before he can act on the contents, Ackroyd lies dead, an antique dagger in his back. Many people came and went from his house that night, but it fell to another resident of King’s Paddock to find the truth. An odd Belgian character who only wanted to grow vegetable marrows…

The third Poirot novel and the fourth book to be released, this is the first book not to feature Hastings, who has gone to the Argentine. Poirot does opine that he misses him as “At times he has said something particularly foolish, and behold that foolish remark has revealed the truth to me!” He has been living in the village of King’s Paddock for a year – the time is a little obscure initially, as his neighbours seem not to have spoken to him, whereas he has been acquainted with Ackroyd, although that friendship never seems to be mentioned again.

Despite retiring, Poirot doesn’t hesitate to get back in the saddle. Clearly he’s forgotten some of his habits, scrabbling around in the dust and fishing in a pond for physical clues. He falls back into more familiar behaviours later, drinking hot chocolate for example, and for the first time, in the books at least, takes the law into his own hands.

As a mystery, it’s very well constructed, with many suspects, most of whom get something to do with the plot. There is an interesting question about how interesting the mystery is without the thing that I’m not going to mention, as the set-up is pretty straightforward, but the structuring of the cluing is excellent. I’d say that even without the thing, it’s not obvious who the murderer is, it’s just an extra layer in the mystery.

There were apparently two inspirations for the format of the tale, either her brother-in-law James Watts or Lord Mountbatten, both of whom suggested the basic idea. Christie has also acknowledged the unsolved murder of lawyer Charles Delauney Bravo in 1876.

It’s often referred to as Christie’s greatest novel – And Then There Were None is the other usual contender – and topped the Poirot poll that I ran a while ago. While it’s not my absolute favourite Poirot tale, it fully deserves its reputation and if you haven’t read it, you really, really should.

Ranking Poirot (so far):

1. The Murder Of Roger Ackroyd
2. The Mysterious Affair At Styles
3. The Murder On The Links
4. Poirot Investigates

Pretty easy choice, that.