Missing Bones — Phyllis J. Perry

Ricky and his chubby beagle, Bones, don't fit in. Ricky is trying to be a good sport about his mother's recent marriage, but his new step-sister Annabelle and her cat are hard to take. Even when Bones saves the cat from a mountain lion's attack, Annabelle blames Bones for the mountain lion being there at all. When Bones goes missing in a thunderstorm, Ricky is frantic. This is a book about family love and adjustment, and the tie between a boy and his dog.