Richard Abernethie has just passed away, and the family has gathered to send him off to his final resting place. At the gathering afterwards, awkward younger sister Cora Lansquenet commits another of her many faux pas, saying that "surely he was murdered?" But when she turns up murdered just a couple of days later, perhaps there was something in what she said? Luckily, the family solicitor is friends with a certain Belgian detective...
As I said above, this is an excellent mystery. Sure, there's just the one real misdirection, and if that is seen through, there are very few suspects available, but I don't see many readers seeing through this particular Christie trick.
Poirot doesn't appear until around halfway through the novel, but is very active afterwards, even though his advanced age is alluded to several times. His investigations mainly consist of him chatting with the different suspects, but there's also an appearance by the efficient Mr. Goby, who can procure information about almost anyone, and who provides background on many of the suspects.
While this may not achieve the excellence of several of her 30s novels, this is still a very strong story that any other mystery author would have been proud to have written. I'll rank it 78 out of 100, and simply hope that one of the later novels that I still have to re-read will at least approach this level of greatness.