Multiple Murderers in a Single Christie Title

Out of 66 titles, we have two murderers rather than a single murderer 16 times. Cat Among the Pigeons then is the only Christie book in which we truly have two murderers acting independently of each other as a means of obfuscation where Miss Chadwick and Anne Chaplin are both legitimate murderers. Now turning to the 13 out of 16 books featuring two murderers working together as a murderous pair, this of course is where we get some of our greatest Christie villains. Jacqueline and Simon are the gold standard. That is my opinion anyway."