The Poisoned Chocolate Case

Anthony Berkeley set in 1920s London in which a group of armchair detectives, who have founded the "Crimes Circle", formulate theories on a recent murder case Scotland Yard has been unable to solve. Each of the six members, including their president, Berkeley's amateur sleuth Roger Sheringham, arrives at an altogether different solution as to the motive and the identity of the perpetrator, and also applies different methods of detection (basically deductive or inductive or a combination of both). Completely devoid of brutality but containing a lot of subtle, tongue-in-cheek humour instead, 

The Poisoned Chocolates Case is one of the classic whodunnits of the Golden Age of Detective Fiction. As at least six plausible explanations of what really happened are put forward one after the other, the reader—just like the members of the Crimes Circle themselves—is kept guessing right up to the final pages of the book.