A wild storm ruins the small beach that the Penwinnard boys regard as their own, but it also brings opportunities. Mutty builds a ‘fort’ with the planks washed ashore – a small shelter that is good for playing, good for having a campfire on the beach, and when more serious problems arise, it acts as a centre for meetings and discussion. The Penwinnard boys have to act together, they have to be clever, and they have to be persistent.