And Then There Were 61: The Murder of Roger Ackroyd by Agatha Christie

Ah, finally, our first real classic. A great, inventive,
rule-breaking classic. Before there was "Gone Girl," our inimitable
Dame Agatha was playing the long narrative con. Plus, we get Poirot
in all his masterful gamesmanship, sly as ever. A certain murderer
may have wished that mustachioed Belgian had never retired and gone
to grow vegetable marrows, but we (and justice seekers everywhere)
are so much the better for his countryside foray.