Yesterday, on All Things Considered, I heard a story about how Philadelphia and Baltimore are fighting over the remains of Edgar Allen Poe. It was mentioned that Poe is considered to be the father of the detective story. Although Poe wrote about cats, and ravens, and what have you, I don't think he ever thought about using an animal detective in a story.
In recent years, there have been a number of writers who have written series that have animals solving, or helping to solve, a mystery. And these are not books written for children! Authors who use cats in detective role are Shirley Rousseau Murphy who has written the Joe Grey series. Joe Grey is a cat who speaks human. Joe appears in Cat Fear No Evil [MYS MUR], Cat to the Dogs [LP MYS MUR], and Cat Laughing Last [MYS MUR], to name just three. And for those who like a little romance with their mystery, you'll be happy to know that Joe has a girlfriend--Dulcie.
Lilian Jackson Braun has written more than two dozen books featuring her human character, Jim Qwilleran, also known as Qwill, and his two cats, Koko and Yum Yum. We have quite a number of books in the "Cat Who..." series, such as The Cat Who Dropped a Bombshell. We have this particular title in three formats--regular print [MYS BRA], large print [LP MYS BRA], and audio [AB/CD MYS BRA].
Writer Rita Mae Brown claims to have co-authored with her cat, Sneaky Pie Brown, a series with a tiger cat, Mrs. Murphy, playing sleuth. Catch as Cat Can [MYS BRO] is one title.
Two other cat series to look for are the "Midnight Louie" books by Carole Nelson Douglas, and the "Big Mike" series by Garrison Allen.