They caught up with him in Belgrade. The aliens had gone by then, only a few shining metal huts in the Siberian tundra giving mute evidence that they had been anything other than a nightmare. It had seemed exactly like that. A nightmare in which all of Earth stood helpless, unable to resist or flee, while the obscene shapes slithered and flopped over all her green fields and fair cities. And the awakening had not brought the reassurance that it had all been a bad dream. That if it had happened i