Professor Bernard Quatermass comes out of retirement to battle sinister forces that are threatening earth.

Following the devastation at Ringstone Round, Quatermass hears of similar incidents worldwide and returns to London. En route they become separated during a shootout with rival gangs.

More and more young people are joining the Planet People, including the gangs that have been terrorising the cities and the soldiers assigned to keep them away from the Megalithic sites.