Bran Mak Morn, King of the Picts, vows revenge on the Roman governor Titus Sulla after witnessing the crucifixion of a fellow Pict. He seeks forbidden aid from the Worms of the Earth, a race of creatures who Bran Mak Morn's pictish ancestors had banished from the earth. They were once men but millennia of living underground caused them to become monstrous and semi-reptilian.