Tiny Tough (Dory Fantasmagory, Bk. 5)

When her big sister Violet has friend trouble at school, Dory tries to come to her rescue. But Dory's active imagination takes over, and she is sure that Violet's lost treasure (a friendship bracelet) has something to do with pirates. In search of the treasure, Dory meets up with a real pirate crew and finds that a pirate's life is harder than she thought. At sea, Dory longs for her imaginary friend Mary. But Mary has gone off with an exciting new friend of her own and Dory is crushed with jealousy. Just when things can't get any worse, Dory's old enemy, Mrs. Gobble Gracker shows up and Dory's ocean adventure takes a surprising turn.