While holidaying with his friend Felix on the island of Innis na Ri in South West Ireland, Chris meets Kaia who belongs to a travelling family.

Kaia was friendly with Mr O'Driscoll, the last owner of the big house where Felix's mother is caretaker.

He claimed to be descended from the last kings of Ireland and was rumoured to be very rich.

When O'Driscoll's descendants decide to sell the island to developers, so depriving Felix's family of a home, the children are determined to search for O'Driscoll's treasure - but they face a race against time.