One, Two, Buckle My Shoe (1940)

PLOT: Someone really doesn't like dentists.


This book is about remarkable coincidence. You can buy that a murder happens whenever Poirot goes on holiday, just as Jessica Fletcher's friends probably check in with their solicitors every time she announces she's dropping round.

By now, of course, you'd assume that if you were planning a murder and you realise that Poirot is on holiday with you, you'd have second thoughts. Similarly, if you're a rich heiress with a persecution complex and Poirot turns up, you'd either jump off the train or summon a priest.

At first glance, this book takes that on the chin. Poirot isn't on safari but mundanely at the dentist. This is an everyday creepy setting and a great place for a murder... but...

The chain of coincidence that this book then requires is remarkable.

• Poirot has a dentist. Fine.
  
• He shares this dentist with the most powerful financial brain in Britain. Also fine - after all, why not specialise in clever teeth?
  
• Although one of your clients is Miss Sainsbury Seale, who is very dim.
  
• And she just happens to know a powerful secret.
  
• She also just happens to have met a powerful blackmailer who just happens to have toothache.

So, just a few pages in, remarkable machinery has been set in motion and the murderer is presented with a most remarkable opportunity that will change the country's future. It's too good to miss. But, and you should remember this... this is also Poirot's dentist!

For the book to succeed, and it does succeed, Christie lays on top of this coincidence a remarkable number of layers of complexity.

So, as well as the dentist at the centre of the universe we have impostors, super secret spies, mysterious organisations, false telegrams and suspicious fiancees as well as at least one death which is almost motiveless.

This is a book stuffed full of herrings, some of them painted a magnificent red which is patiently washed off by Poirot, leaving you, by the end, aware that the book is about something you really didn't think it could be about.

The framing device of the nursery rhyme adds to the splendid conclusion - it has almost nothing to do with the story, and yet, by the end, you realise it has everything to do with the solution.

The book also re-poses the question of necessary murder to Poirot. Is there such a thing as a crime that is so important that justice cannot be brought? Not in Poirot's eyes. Curiously, the ITV adaptation implies that, by making this choice, Poirot causes the second world war. Which seems a little unfair.