Ed Bronson thought it out on his way to the police station. Man was an impossible mixture of altruism and selfishness. Man was inclined to give freely to those who were needy--but would fight like fury to withhold the very smallest of his possessions from the avaricious grasp of those who would wrest them from him by force. As a world requiring pity, aid and mercy, every effort would be bent towards that end, even to the job of making room for them in an already crowded world. But they had entered like bank robbers or claim jumpers. Their own world lost, they intended to abandon it, pirating any other world they could. The brotherhood of man collapsed at that point and became a brotherhood of hate. Tolerance and mercy and willingness to offer succor must be forgotten when the needy become vicious. Biting the hand that feeds is an old platitude which still holds true. So Ed Bronson knew that, regardless of their wretched situation, they must be stopped. This was invasion with capital letters. Even though many of them must be direct descendants of people in this world, invasion meant war! Even worse than civil war was the brother against brother, man against man, war of survival. They--and Ed Bronson paused. 'They' was an indefinite term. 'They' should have some nomenclature for purposes of identification. Were the invasion from another planet, 'they' would have a name. Were it merely an earthly war, country against country or political clan against political clan, both sides would have names. But here was a case where it would be one earth, one world, against another world--identical save for a trick in time that had split them apart. Bronson needed a name and he needed it quickly. He reasoned and came to the conclusion that the 'other world' should be called Earth Two because it was not long for living. Once it was destroyed by its own fire this world would revert to being '_the_' earth. Until such a time as differentiation became unnecessary he would call the two worlds Earth One and Earth Two. Thus, independently, did the people of three almost identical earths arrive at the same conclusion. Earth One was the original, where the Alamogordo Experiment had been successful. Earth Two was where the million-to-one chance of starting an all-consuming atomic fire had actually happened. Earth Three was where the Alamogordo Experiment had failed. Ed Bronson and the folk from Earth Two were still to learn of Earth Three and it was only sheer reasoning that made all three systems of nomenclature congruent. So by the time Ed Bronson located the police department he was prepared to give a coherent story. He asked for the captain in charge. "Cap'n Norris is busy," grumped the desk sergeant. "What's the matter?" "My home is being invaded and--"