Marnie Blue's adventures at Lady Sealia Foam's Mermaid School continue! Marnie is super excited because she's going on a field trip to see the legendary palace of Queen Maretta with all her friends. But when her mom gets sick and can't join the trip, Aunt Christabel agrees to come in her place--which is just a recipe for disaster! Christabel Blue is o-fish-ially the biggest troublemaker that the school has ever known. Will they board the whale-shark on time? Will the palace tour go off without a hitch? And just who is sneaking around the palace causing all the mischief?