The Mystery of the Wrong Dog (Three Cousins Detective Club)

is #3 in the Three Cousins Detective Club series.
==Book Description==
In The Mystery of the Wrong Dog, Titus McKay has been placed in charge of his elderly neighbor's crabby Yorkshire terrier, Kingsley and Titus plans to show his parents he's ready for a dog of his own. But suddenly grumpy Kingsley turns into a sweet, lovable dog! What happened to Kingsley? It's up to Titus, Timothy, and Sarah-Jane to solve the mystery!
(Description from paperbackswap.com)