The Black Spectacles (British Library Crime Classics)

Everything you could ever want in a Golden Age of Detective Fiction novel. ― Booklist
Also known by its US title The Problem of the Green Capsule, this classic novel is widely regarded as one of John Dickson Carr's masterpieces and remains among the greatest impossible crime mysteries of all time.
A sinister case of deadly poisoned chocolates from Sodbury Cross's high street shop haunts the group of friends and relatives assembled at Bellegarde, among the orchards of 'peach-fancier' Marcus Chesney. To prove a point about how the sweets could have been poisoned under the nose of the shopkeeper, Chesney stages an elaborate memory game to test whether any of his guests can see beyond their 'black spectacles'; that is, to see the truth without assumptions as witnesses.