Nugget comes back from school with a drawing of a beautiful mermaid, but Jim laughs and takes him on a trip to see a real mermaid.

Jim and his family seem to have fallen victim to a curse, and decide to go back to sea; if not, they are in danger of being turned into landlubbers just like their house, which is magically cleaned and nicely decorated in their absence.

In Dull-on-Sea, Matilda finds her quiet life commandeered by the arrival of an eccentric pirate family, the Jolley-Rogers, and she quickly befreinds them.

To his horror, Jim discovers his ancestry isn't with infamous pirates, but from Francis Flunky, an expert on etiquette; Jim then tries to behave as an upstanding, polite young boy.