This introductory scene is a fine thriller opening, and other thriller authors have used similar opening scenes to their stories. What differenciates this book from those other thrillers is that this is not a story. It's a whole mess of incoherent scenes that amount to nothing in the big picture. Anything that happens in the overarching plot (such as it is) happens offstage and is reported by characters in the opening of the next chapter of the book.
I'm reminded of Colin Forbes's late career works when I read this one. Everything in the world is one huge conspiracy, and the increasingly conservative authors seem as out of touch with reality as is humanly possible, seeing ghosts and ghoulies in everything around them.
This novel is as disjointed as the more infamous Postern of Fate and deserves as little consideration as that novel does in Christie's oeuvre - or less. It's a wonder that the intermediate Nemesis and Elephants Can Remember turned out as well as they did - even the latter, which is not particularly favourably seen, is eminently readable compared with this novel and, perhaps more importantly, much more coherent.
There are individual scenes here that arouses the reader's interest - Nye's travels to Bavaria/Austria/wherever, and Lady Matilda's visit there later come to mind - but ultimately they develop into nothing, and the disappointment almost worsens because of that.
Bit characters like Colonel Pikeaway and Mr. Robinson feature in this book, which means that they hold the ignominious distinction of being in almost every pointless Christie novel (they're in this one, Cat Among the Pigeons and Postern of Fate, and Robinson turns up in At Bertram's Hotel as well). Let's all blame them!
I'll award this a 2 out of 100, it's Christie's worst novel and should not be read by anyone.