At Entertainment Weekly, there is a post on the Halloween episodes of The Mentalist and Castle, both fun shows indeed, and the writer mentions the Transitive Property of Evil--that a character actor that is evil on one show is the likely killer on another show. I sort of agree with this, but there is the more fundamental rule--the Kathy Saideman rule of fiction that has ruined me forever.
The Kathy Saideman rule of fiction refers to the identification of key props or individuals early in a tv show or movie that will have to become relevant later on. I can now almost always identify the killer or key object upon which the plot ultimately turns early, thanks to my instructions at the plot master.
Lesson, as always, is either: a) the wife is always right; or b) don't marry an editor.