[1] Siblings Julian, Dick and Anne have come to Kirrin to spend the remainder of a school holiday with their tomboy cousin, George, and her dog, Timmy.

Two scientist colleagues of George's father, Uncle Quentin, visit Kirrin Cottage to work on an alternative energy project.

George takes an instant disliking to Berta, especially as the American girl has brought her dog, a poodle called Sally.

A few days later, Uncle Quentin receives an urgent message to meet with Elbur to discuss calculations for their energy project.

Jo's friend at the fair, Spiky, points them in the direction of Gringo's caravan, where George had until recently been held captive.

Julian enlists the help of a local garage worker, Jim, to find out the recent movements of Gringo's distinctive car.