There must at the dénoument be surprise, & yet the surprise must not be complete. Hence the criminal must not be an outsider of whom we've hardly heard.
Nor
he must not be
the detective, unless the detective[,| w]as unless made out the sort of man, one might have suspected[;|.] the criminal must not be Nor the nice young man, or nice young woman to whom during the whole course of the story we wish happiness[,|:] [o|O]n the other hand he must not be the man
9
we've one obvious suspect. These rules are very stringent & leave only a very
narow
small
margin for the writer, as it were a tiny dance floor on which to perform.