The fourth story in the series sees the Five planning their Easter holidays at Kirrin, but a terrible storm in the night sends a tree crashing down on Kirrin Cottage resulting in very serious damage. Because of this, everyone has to find an alternative place to stay for the holiday.
Uncle Quentin arranges for the Five to stay with a friend of his, a Mr Lenoir, who is interested in the same work as he. Mr Lenoir has a large rambling house in the town of Castaway called Smuggler's Top. He also has two children one of whom, "Sooty" Lenoir, is a pupil at Julian and Dick's school.
Unfortunately for George, Mr Lenoir had insisted that no pets were allowed, but George planned to sneak Timmy in so the Five set off to finish their holiday there.
Of course, George causes chaos with Timmy having to hide him within secret passages of the old house. The Five also fall foul of Mr Lenoir's sinister man-servant, Block, who
constantly watches the children in the hope of catching them red-handed with Timmy.
"Sooty" Lenoir shows the Five a mysterious light flashing from one of the towers one night, and the Five, suspecting that smuggling is still going on in Castaway, set about
catching the culprits. But when both Uncle Quentin and "Sooty" disappear, events become very serious indeed.