I got distracted by something or other last year, but am beginning a full Agatha Christie reread, going through all her books, 82 on the American plan, and seeing how long it takes me to see it through.
As I type this, it is 00:14 am, January 31.
This is the copy of The Mysterious Affair at Styles that I own. The book was first published in 1920; this edition is from 1991. It is narrated by the character Hastings, who is a friend of our newly-introduced detective, Hercule Poirot. Hastings is very Dr. Watson-like, but Poirot is more arrogant, yet less aware of it, than was Sherlock Holmes.
This book is in the public domain and you can find it here at Project Gutenberg. It's a pretty easy story to read and follow. You discover all the clues right along with Poirot, but won't necessarily put them together as he does until the very end.