The Bamboozlers — Michael de Guzman

Albert Rosegarden is a boy ready and waiting for an adventure to take him away from Mountain View, Idaho (where there are no mountains in view)--and he gets what he wants when Wendell shows up, the grandfather Albert didn't know he had. Wendell is an old ex-con of mixed ancestry who carries a violin case he calls the Stradivarius. Albert's mother and Wendell have been estranged for years, and she orders him to leave immediately. But Albert talks her into letting his grandfather spend the night. Which is the beginning of the adventure Albert yearned for--an adventure that takes him and Wendell and a three-legged dog to Seattle, where they are going to pull off the perfect con--the conning of a con man.
The author's irrepressible and inventive third novel is about love and the passing of wisdom; as Wendell puts it when he and Albert first see Seattle, "This is going to be the most fun you've ever had."