Did you know that there are three classes of mystery?
(1) Fair-Play Whodunnit: We play along with the detective, solve the crime as the main character does.
In 1928, the writer Father Ronald Knox created a "Ten Commandments" of plot devices (Knox's Decalogue) that more or less codified the rules of the Fair-play whodunnit:
- The criminal must be someone mentioned in the early part of the story, but must not be anyone whose thoughts the reader has been allowed to follow.
- All supernatural or preternatural agencies are ruled out as a matter of course.
- Not more than one secret room or passage is allowable, and such a passage may only be in a house or building for which it is appropriate by age or purpose.
- No hitherto undiscovered poisons may be used, nor any appliance which will need a long scientific explanation at the end.
- No Chinaman must figure in the story. (I don't know why this rule exists.)
- No accident must ever help the detective, nor must he ever have an unaccountable intuition which proves to be right.
- The detective must not himself commit the crime. (I think Agatha Christie broke this rule.)
- The detective must not light on any clues which are not instantly produced for the inspection of the reader.
- The stupid friend of the detective, the "Watson", must not conceal any thoughts which pass through his mind; his intelligence must be slightly, but very slightly, below that of the average reader.
- Twin brothers, and doubles generally, must not appear unless we have been duly prepared for them.
(2) The Clueless Mystery: We just have to read along because the writer doesn't provide enough clues for us to solve the mystery.
Example of a Clueless Mystery: Right from the beginning in A Study In Scarlet, despite Holmes describing the murderer's appearance and even how he got to the scene of the crime in detail from the clues in the room, nobody even slightly resembling the murderer turns up until the last chapter of the London-based narrative.
(3) The Reverse Whodunnit: We know who did and how it was done. We just have to read to the end to see if justice is served or if the criminal gets away with the perfect crime.
Example of a Reverse Whodunnit: Red Dragon and its sequel, The Silence of the Lambs. In both of them, we know fairly early on who the killer is, and learn more details as the FBI protagonists figure out the mystery.
What is your favorite type of mystery? What examples do you have of that type?
Source: TV Tropes
Photo credit: Creative Commons Attribution 2.0 Generic (CC BY 2.0)