The Murder of Roger Ackroyd by Agatha Christie

(From Goodreads)

Considered to be one of Agatha Christie's greatest and also, most controversial mysteries. 'The Murder Of Roger Ackroyd' breaks the rules of traditional mystery.

The peaceful English village of King’s Abbot is stunned. The widow Ferrars dies from an overdose of Veronal. Not twenty-four hours later, Roger Ackroyd—the man she had planned to marry—is murdered. It is a baffling case involving blackmail and death that taxes Hercule Poirot’s “little grey cells” before he reaches one of the most startling conclusions of his career.