The Big Four is not a traditional Poirot mystery. It isn’t structured as a straight novel, but as an interconnected set of short stories. And these were short stories that Christie had already written. She had previously published them as a short story collection called The Man Who Was Number Four (published 1924). The novelisation of the short story collection involved mainly revising the beginnings and endings of each story to make them work together as a novel. Christie later described it as “that rotten book” in a letter to her agent in 1942. Christie needed money and was struggling to write, due to everything that was happening in her life at that time. Her brother-in-law, Campbell Christie, suggested the novelisation of the short stories rather than struggling with a new novel, and he helped her prepare them for publication.

The Big Four is told from Captain Arthur Hasting’s viewpoint. After being away in Argentina for some years, Hastings is back by Poirot’s side for this book. The book opens with his return to England, home for business reasons and looking forward to seeing his old friend. But he is surprised to find Poirot about to leave on a long trip – just as Hastings has arrived in England to surprise Poirot, Poirot is about to journey to Argentina, to surprise Hastings. While they are exclaiming over each other, a mysterious stranger turns up in Poirot’s bedroom. He dies, but only after telling Poirot about an international crime cartel, known as the Big Four.

Of course, Poirot and Hastings start to search for this Big Four. All they have to go on is that No. 1 is Li Chang Yen, a Chinese political mastermind; No. 2 is wealthy, probably American; No. 3 is a French woman; and No. 4 is known as the Destroyer: all this from the man who died in Poirot’s apartment. It’s not much to go on, but Poirot gradually starts picking up leads and weaving them together, leading him to understand that the Big Four have a goal of world domination. It’s all pretty standard fare for a spy thriller, but not what Christie was known for. The book at times seems like a modern conspiracy theory, about a mysterious group of elites who secretly control all world events for their own ends. But it is a story that does fit in with the general unrest in Europe following World War I and the social unrest of the 1920s.

Most of the stories that make up the book are murders. They seem unconnected, but Poirot figures out in each case that they are the work of No. 4, the Destroyer. In each case No. 4 has used a disguise so well done that no one can penetrate it, or tell what he really looks like. Using one disguise he impersonates a doctor, a locum standing in for the regular village doctor, solely so he can kill one of the patients. He plays his part so well that no one picks that he isn’t a doctor, despite presumably him having to deal with a lot of patients/medical conditions, as it mentions that he has been there for a month. Poirot has to constantly react to changing circumstances, rather than methodically work his way through a single crime. And there is never time for any subtlety to the stories. They each need to be finished quickly so we can move on the next one in this cat and mouse game. This is fine when you know you’re reading a short story collection, but it is a bit jarring when you are reading a novel. And of course, Poirot isn’t even catching the murderer in any of the cases. The best he can manage is to clear suspicion from whoever No. 4 has set up to be the murderer in that chapter.

Several of the stories do advance the main plot. In one, Poirot investigates a missing British scientist, and he learns the identity of No. 3. In another, where Poirot plants Hastings in a job as secretary to a wealthy man, he confirms his suspicions about the identity of No. 2. And finally, one story towards the end of the book gives us the name of No. 4, even if Poirot still doesn’t know what he looks like.

Hastings is, as always, the slightly dim companion who gives complete support to Poirot, even as he suffers under Poirot’s insults about his intelligence. At one point they both narrowly escape death from a falling tree when Poirot observes “Yes, but for my quick eyes, the eyes of a cat, Hercule Poirot might now be crushed out of existence – a terrible calamity for the world. And you too, mon ami – though that would not be such a national catastrophe”. But as this is the same chapter that has Hastings think, “It has always seemed to me extraordinary that a woman should go so far in the scientific world. I should have thought a purely masculine brain was needed for such work.", I wasn’t inclined to be too sympathetic to his feelings. [Toriaz has an Honours Degree in Physics – bikerbuddy (ed.)]

The separate murder investigations and occasional plot advancements can’t last forever, and eventually we get to the point where Poirot has pieced together all the threads of information he has gathered (many of which are gathered outside the scope of the story and are just referred to in passing by Poirot or Hastings), until we get to the final showdown between Poirot and the Big Four. In true thriller style, Christie has a couple of twists saved for the end to stop you from guessing exactly how this will go. It all combines to be a fun read, but it’s position near the bottom of most people’s lists of favourite Christies is well deserved. It just isn’t as good as many of her other books. It’s a bit disjointed, and it’s not a mystery where readers can play along and try to guess who will be the murderer. There is never any doubt about who the bad guys are, we even know most of their names very early in the story because it’s not about solving a murder, it’s about stopping this group from taking control of the world. So overall, it’s a fun read but not one I’m likely to recommend as a good Poirot story.