10. The Ubiquitous Sidekick
Batman has Robin, Poe’s C. Auguste Dupin has the unnamed narrator, House has Kutner, 13 and Taub. Every detective has the Sidekick who seems superfluous, but in fact, he is critical to both the detective and the story. The sidekick’s presence lends an excuse for everything to be explained and reviewed, endlessly almost to idiocy.

11. Rationalism
The clues, the crime, the culprit, everything must be explained rationally. It would be cruel tricks of the author if the solution were one the typical reader would never, or could never, have logically arrived at himself. The reader wants to enjoy the process of being presented with a rational case, with clues and a solution he is capable of noticing himself.

12. Everything is Critical
A note of caution. Never overlook any element of the story, not a character or comment. Usually, almost predictably, the solution is one the author tried to have the reader ignore.