Marnie Blue is so excited! She is going on a school trip to see the legendary palace of Queen Maretta with all her friends. But when Mum is too unwell to join the trip, Aunt Christabel agrees to come in her place, and she was ‘offishially’ the naughtiest mermaid the school has ever known. Marnie expects mayhem. Will they board the whale-shark on time? Will everyone eat their packed lunches on the way there? And just who is sneaking around the palace causing all sorts of mischief?