This film chronicles the story of the Walker children on their holidays in the Lake District in England. They want to camp on an island in the lake. When they get there in the boat Swallow, they soon discover they are not alone. Two other children, the Blacketts, also known as the Amazons, have set up camp there, and a battle for the island begins. But with Britain on the brink of war and a secret agent looking for the Blackett children’s uncle, they have a series of adventures quite different from their plans.