Probably The World's Best Story about a Dog and the Girl Who Loved Me — D. James Smith

But then the family dog, Rufus, is stolen.

Overnight, Paolo is trying to manage not just Georgie, but their deaf cousin, Billy, who speaks only with his hands; Henry, a strange vacation visitor whom the boys discover living locked in his aunt's attic; and Butter Schwartz, a lonely, half-wild schemer with a paper route. The last two are definite dognapping suspects....

To top it all, a girl with a big-time crush on Paolo won't let him be, day or night, crisis or no crisis. For her, missing Rufus is nothing to snaring Paolo, who has met his match as a manager.

The solution to the mystery of Rufus, the threat of Theresa, and the future must rest in Billy's hands.