Mariella Mystery (That's me!) - totally amazing girl detective, aged 9 and a bit. Able to solve the most mysterious mysteries and perplexing problems, even before breakfast. When their teacher Miss Crumble spots the ghost of her pet guinea pig, Mr Darcy, in her back garden, she doesn't know what to think. But Mariella knows it's up to her and her fellow Mystery Girls to get to the bottom of The Case of the Ghostly Guinea Pig.