Reissue of one of the great puzzle mystery classics of England's Golden Age of crime fiction; plot involves a group of upper-crust amateur sleuths who set out to solve a murder that has baffled Scotland Yard; catnip for fans of Agatha Christie and Margery Allingham.

After arriving at his London club at 10:30 am precisely, which he has been doing every morning for many years, Sir Eustace Pennefather, a known womanizer whose divorce from his current wife is pending, receives a complimentary box of chocolates through the post.
Disapproving of such modern marketing techniques, Sir Eustace is about to throw away the chocolates in disgust but changes his mind when he learns that Graham Bendix, another member of the club whom he hardly knows, has lost a bet with his wife Joan and now owes her a box of chocolates.
Bendix takes the box home and, after lunch, tries out the new confectionery together with his wife. A few hours later Joan Bendix is dead, whereas her husband, who has eaten far fewer chocolates, is taken seriously ill and hospitalized.

(From Goodreads)