The criminal must be mentioned in the early part of the story,
but must not be anyone whose thoughts the reader has been alowed to follow.
All supernatural or prenatural agencies are ruled out as a matter of course.
Not more than one secret room or passage is allowable.
No hitherto undiscovered poisons may be used, nor any appliance
which will need
a long and scientific explanation at the end.
No Chinaman must figure in the story
No accident must ever help the detective, nor must he have an
unaccountable intuition which proves to be right.
The detective himself must not commit the crime.
The detective is bound to declare any clues upon which he may happen to light.
The stupid friend of the detective, the Watson, must not conceal from the reader
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
Move onto The Hard Boiled School of Detective Fiction