The Nine Mile Walk by Harry Kemelman.
Characters: Two men, Nicholas Welt and the unnamed man who relates the tale.
Setting: Two men have breakfast at a restaurant called The Blue Moon and afterward head to the narrator's office.
Plot: It's just a conversation that starts with a bet and ends up solving a murder.
How it starts: Nicky says: "An inference can be logical and still not be true."
Then he says: "Give me any sentence of ten or twelve words and I'll build you a logical chain of inferences that you never dreamed of when you framed the sentence."
So the main characters says: "A nine mile walk is no joke, especially in the rain." From that eleven word sentence, Nicky solves a murder. It's one of the most amazing stories I've ever read.