The Stranger Next Door — Peg Kehret

If there's a mystery to be solved, Pete's your man. Er, your cat. Pete's a cat, specifically, Alex's cat. And since Alex and his family moved into a new housing development, Pete is Alex's only friend. Things start looking up for Alex when Rocky moves in next door. But Rocky isn't very friendly, and Alex starts to suspect he's hiding something. And when the neighborhood is terrorized by a rash of fires and vandalism, Pete knows that he's got to investigate.