How to do mysteries - the three clue rule

This is very short post. I'm just going to give you the link to Justin Alexander's great post about designing mysteries. He lays it out nice and tidy how to make a design with multiple paths. I found the link to it in the comments on Grognardia's discussion about railroady CoC campaigns. If I decide to sit down and write a CoC mystery it will be better now that I've read his essay! Go read it!