Mystery

A genre built on withheld information.

Mystery reverses normal narrative order. The central event has already happened, and the plot is the reconstruction of it. The reader's pleasure comes from being given enough to solve it and not quite noticing.

Fair play

The classical convention is that every clue available to the detective is available to the reader. A solution turning on information never shown is a breach, which is why so much of the craft is in disguising clues rather than hiding them.