The A.B.C. Murders (Hercule Poirot, #13)
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What one recalls vividly, after several decades and more - not half a century yet, perhaps - of having read most of Christie, including this, is about how a good detective reads about the alphabetical order of three murders happening, manages to guess the next, and solves which was the real one, thereby solving who was behind it all - alphabetical twist being merely to throw dust in the eye, so to speak.
If one recalls correctly, D was real, E was prevented, and case solved.