Hideout by Gordon Korman

Griffin Bing, his friends, and Luthor, the 150-pound Doberman are back for another zany adventure.  S. Wendell Palomino, or "Swindle" as he was called by the friends in the first book, tries to regain ownership of Luthor.  Swindle not only wants Luthor back, he wants revenge.  Griffin devises a plan to keep this from happening.  The plan involves hiding Luthor at the different summer camps the kids are attending, but problems begin and the efforts to stay ahead of Swindle's plans provide plenty of adventures and laughs.  For those who haven't read the previous four books in this series, the author provides a short recap at the beginning.  However; after reading this book, I'm betting that you'll become a fan and will want to go back and read the first four books.