To Slay a Man about a Dog — Fredric Brown

Peter Kidd should have suspected the shaggy dog of something, right away. He got into trouble the first time he saw the animal. It was the first hour of the first day of Peter Kidd's debut as a private investigator. Specifically, ten minutes after nine in the morning...

"Fredric Brown (1906-1972) was an American science fiction and mystery writer. He is perhaps best known for his use of humor and for his mastery of the "short short" form--stories of 1 to 3 pages, often with ingenious plotting devices and surprise endings. Humor and a somewhat postmodern outlook carried over into his novels as well." -- Wikipedia