Okay. I need to know who was the murderer of Roger Ackroyd and Ms. Ferrars, how the murderer was captured, and also what were the murderers motives. Please I just need the bare minimum of what happened - just the big important facts.
Dr. Sheffield is the murderer of Ackroyd and Ferrars, even though he appears throughout the story to be the impartial narrator. He was captured mostly through the process of elimination, having himself helped Poirot to discard all the other suspects as not guilty. Christie took much criticism as a mystery author by tricking her readers at the end and revealing the narrator to have lied throughout the novel, but most people accept her clever handling of the crime. Blackmail was the motive.
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