Mr Shaitana regards crime as an art, especially if the murderer is not convicted. One day he invites Poirot to a dinner party where he shall meet four successful murderers. Apart from these people, there are also Superintendent Battle, Colonel Race and Mrs Oliver. During their dinner, Mr Shaitana starts talking about opportunities to commit crimes that are never detected - and by the end of the evening he is dead.
Poirot, Battle, Race and Mrs Oliver start their investigations - and are faced with the problem that any of the four others had a chance to kill Mr Shaitana. To discover the truth, they have to find out what murders they committed in the past that Mr Shaitana could have known about...
The brilliant thing about this book is that there are only four suspects and hardly any facts to go upon. There are no clues in the room that indicate a certain person, nor is there any question of time. The crime has to be purely solved by psychology - Poirot's favourite way of looking at things.
I thoroughly enjoyed the book (especially since I guessed the right solution), and I recommend it to anyone who likes to approach a mystery from the psychological angle. If you prefer lots of clues, you probably won't like that book very much.