The Big Four
This was the fifth Poirot book and was first published in 1927. Some people have suggested it was the result of a number of short magazine stories having been cobbled together and it certainly is not regarded by most fans of Agatha as one of her finest books. Some people have suggested that the trials and tribulations she was going through at the time are reflected in the quality of the book.
The plot is unlike any other Poirot story in that Poirot and Hastings are battling four super villains known as the Big Four. It is a disconcerting story as it has echoes of Sherlock Holmes and his battles with Dr Moriarty and pressages the later novels that feature British agent James Bond. Having been written in 1927 it is also quite an odd period for a modern audiencce to come to terms with. The Russian Revolution and the horrors that followed it are really uppermost in peoples' minds as far as international politics is concerned. The First World War and its aftermath are also very fresh in peoples' minds and China is still a closed and distant society decades away from the eventual Communist takeover by Mao.
The genre aside, fans are also quite critical of the characterisation of the Big Four. There is no real adequate explanation of their motivation nor of how they came to be working together. They seem to have a supernatual ability to outwit Poirot whose repeated retort is that each time they win it teaches him something more about them and thus helps in his ambition to defeat them.
The book is worth reading for no other reason than that when set against her best works it shows just what a master storyteller she was. Most authors have weaker works and when their output was as great as hers, it is hardly a surprise that the odd one is not up to par.
You can see what fans of Agatha Chrsitie had to say about the book by clicking here