Before the review I just want to ask a couple of questions. What was The Queen of Mystery smoking? It this stuff still available in 21st century?
On to the review: the only reason I can justify the existence of this abomination is that it is a parody (I hope it is) of Sherlock Holmes vs. Prof. Moriarty duel of wits. Basically, there is an international crime cartel led by 4 people the last of whom is a ruthless killer whose identity is unknown. It is up to Poirot and Hastings to track him down. It is a collection of seemingly unrelated cases with guy #4 being the culprit. I also need to mention that the most part of the last case is taken almost word-by-word from first half of Sherlock Holmes' The Final Problem with substitution by names. While the original is a very tragic story, this one reads as a buffoonery.
The book is a disgrace of Hercule Poirot. I am a big fan of him, and the next worst Poirot story gets solid 4 stars from me, but try as I might I cannot bring myself to give this one more than 1 star. Avoid it if you have not read it before, even if you are a die-hard fan.