Synopsis: From the back cover of the Ballantine first edition: "In the era of Anti-Matter. When the scientists of the wandering planet HE - in their journeys through the farthest reaches of inter-galactic space - heard the sounds of hydrogen atoms coming into existence out of nothing, they realized that they had accidentally discovered the birthplace of continuous creation. But they didn't know until later, much later, that they had uncovered mankind's Day of Judgment. Following up on the Hevians' discovery, scientists of New Earth learned of the existence of a Universe based on anti-matter - a chemical and physical structure so antagonistic to their own Universe that the slightest contact meant instantaneous oblivion for both worlds. In desperation, the scientists joined forces to create a missile to explore this mysterious and hostile anti-matter Universe. But when the missile returned the scientists learned one awesome fact: In three years time the two Universes were doomed to inevitable, catastrophic collision!"