Poirot comes across as rather mean and impatient in this book, lacking his usual pomposity and self-aggrandisement that tends, in the rest of the series, to undercut his arrogance. He's also sort of a minor character in his own final story, which is disappointing. The ending is really good though, and Hastings is always good. And the mystery is interesting and clever, even if it's not particularly plausible.