The Problem of the Green Capsule // The Black Spectacles — John Dickson Carr

A MOST INTERESTING MAN...

He was known as a good fellow, a jovial soul. He was a magnificent actor and exceedingly vain. He prided himself on his intelligence, preened over his looks and manners, thrilled in his ability to deceive and lusted in his power to manipulate others.

A most interesting man but with a lethal flaw -- a fascination with poison!