As you can see, I'm about half-done with the buddy read, and I'm enjoying it immensely, as always. Poirot hasn't yet made his appearance in the book - this is one of his latest arrivals.
However, Tannat's review mentioned that she wondered if it might not have been a better mystery without Poirot, which got me thinking about whether Agatha had considered writing the book with a different detective. I duly dragged out my copies of the Curran books that take us through Christie's notebooks to see if there was an answer there.
The second book, Agatha Christie: Murder in the Making; More Stories and Secrets from Her Notebooks, devotes several pages to Cat Among the Pigeons. There are over 80 pages in her notebooks devoted to CAtP, and in the initial brief book notes, Christie is considering both Poirot and Miss Marple for the detective positions:
Miss Marple? Great niece at the school?
Poirot? Mrs. U sits opposite him in a train
There were also two proposed titles for the book:
Death of a Games Mistress
Cat Among the Pigeons
Obviously, we know which title was picked, although Death of a Games Mistress actually makes it into the story in the conversation between police officers early in the book, after Miss Springer is murdered.
Also, as a little fun tidbit, I can also share that apparently Cat Among the Pigeons was a proposed name for another Christie mystery - Ordeal By Innocence - before it became the title of this mystery.