Curtain: Poirot's last case

It was at Styles where Poirot's investigation begins with Arther Hastings.

Now Poirot summons Hastings again for what poirot knows will be his last case and according to him it is the perfect murder and he will find the ultimate murderer.

There have been five unrelated murders, Poirot is determined to prevent the next murder and execute the death sentence for the murderer.