Nate the Great and the Missing Key — Marjorie Weinman Sharmat

Nate the Great doesn't especially want to go to a birthday party for Annie's ferocious dog, Fang. But he can't resist a mystery -- and when Annie loses her house key and can't get inside to set up the party, Nate and his trusty dog, Sludge, are hot on the trail. Their only clue is a mysterious poem written by Annie's friend Rosamond. But nothing is too tough for Nate the Great -- not even Fang!