During the extension of the London Underground at Hobbs End, workers uncover a peculiar skull and a large metallic object. Dr. Matthew Roney, a palaeontologist, identifies the skull as belonging to an ancient hominid, far older than any previous find. Meanwhile, Professor Bernard Quatermass investigates the metallic object, initially believed to be an unexploded World War II bomb. As the team delves deeper, they uncover evidence suggesting something more, predating humanity.