Workers excavating at an underground station in London uncover the skeletal remains of ancient apes with large skulls. Further digging reveals what is at first believed to be an unexploded German bomb from World War II. Missile expert Colonel Breen is brought in to investigate, accompanied by Professor Bernard Quartermass. When the interior of the "missile" is exposed, a dead locust-like creature that resembles the devil is found. It is determined by Quartermass that these "locusts" are evil Martians who altered the brains of our simian ancestors to eventually lay claim to the Earth. When Quartermass's suspicion that the missile can reactivate the dormant evil in humans is confirmed, all hell breaks loose.