Sophie Hannah - A háromnegyed rejtélye

Hercule Poirot returns home after lunch to find an upset lady at his door, who angrily questions him: why did he write to her, accusing him of killing a certain Barnabas Pandy, whom he had never heard of in his life?
Poirot had never heard of this Barnabas either, and it would never have occurred to him to accuse anyone of murder in a letter. The detective is even more amazed when he finds a strange man in his apartment who claims to have received a letter from him that morning.
And of course he also accused him of murdering Barnabas Pandy in it.
How many more leaves can there be? Who sent them and why? And above all: who the hell is this Barnabas Pandy? Is he still alive? Or was he really murdered? A great case study for a master detective!