Middle-class parents have bought a run-down school in the country. Their two children, plus an assortment of friends, are staying there over the summer. One day an old lady is found in the school, claiming she used to work there. The children hold her to ransom, but no-one takes any notice.

A young boy dies after swimming at a seaside resort, and the local children, led by Gavin, investigate and are led to suspect that contamination from a nearby nuclear plant is to blame. Their teacher is sympathetic, but has broken into her house, perhaps as a warning. Gavin is nearly killed after talking about the problem on TV, but gradually all is uncovered - with terrible consequences for Gavin.