Mabel lives with her parents in The Mermaid Hotel, by the sea. Mabel likes to keep an eye on the comings and goings of all the guests. Then one day a particularly interesting old lady comes to stay. There is something very suspicious about her, with her growly voice and her heavy trunks and her beady-eyed tortoise. And why does no one know her real name? There can only be one answer, Mabel decides – this guest is a supervillain.
