At first it was just another hoax, another UFO story, but the sightings went on increasing. It couldn't be an alien, there had been so many false alarms, dramatic news-columnists had shouted 'wolf' so many times, that John Citizen shrugged his shoulders and said 'nuts' at the very mention of the word space-ship. Then one of them landed... The things they did were not exactly friendly. In fact by the time they'd finished, they had made an old-time Viking raid seem like a social call from the vicar... Many other attacks followed. Day after day and night after night the alien ships screamed in on their mission of death. The earth struck back. But no one could track the aliens to their lair. They seemed to come from Nowhere. They weren't Martians. They weren't Venusians, and they weren't from another system. That left only one place where they could have originated... yet the truth was so fantastic that none of the earth governments would take it seriously until it was almost too late. The enemy came from within From the gigantic caverns at the earth's core.