This book, first published in 1932, was next on my list of Agatha Christie's mysteries in order. On b&n.com, it is listed as #8 in the Hercule Poirot series. I guess at this point Mrs. Christie had decided that she was stuck with continuing to write the Poirot character, after her attempt to retire him in The Murder of Roger Ackroyd.
This is one of her best Poirot stories, in my opinion, because he takes so long to arrive at the solution to the mystery. (In most books he seems to have everything figured out right away, and spends most of the book sneering at everyone for not knowing the answers.)
I have previously read this book, recently enough to be able remember who the murderer was before I was halfway finished, but the story is still very good.
I recently read by this author: The Sittaford Mystery