With the long summer school holidays coming to an end, Rachel Cook's days are filled with hordes of homework and little time for boredom. But on an unusually hot and sticky Wednesday morning, her uneventful school break comes to a shuddering stop: an innocent trip to the park leaves her with more questions than answers about her family's strange past. As her parents' finances plummet towards the poverty line and beyond, the Cooks end up living high above a seaside town, in a creaky treehouse with a leaky loft.

Rachel makes new friends when she rekindles an old one, and together they grapple the odd goings-on around the town of Lower-Inkcome-by-the-sea. With pirates aplenty, a murderer on the loose and a game of marbles hanging in the balance, she finally pits her wits against a most unpleasant stinky bird!