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 in reality, the people of Earth would have been capable of dealing with the terrible menace. It had been real. And they had been no more capable of resisting the giant intelligences than a child of killing the ogre in his favorite fairy story.

It was an ironic parallel, because that was what finally saved Earth for its own people. A fairy story.

The old fable of the lion and the mouse. When the lion had exhausted his atomic armor and proud science against the invincible and immortal invaders of Earth--for they could not be killed by any means--the mouse attacked and vanquished them.

The mouse, the lowest form of life: the fungoids, the air of Earth swarming with millions of their spores, attacked the monstrous bodies, grew and entwined within the gray convolutions that were their brain centers. And as the tiny thread-roots probed and tightened, the aliens screamed soundlessly. The intelligences toppled and fell, and at last that few among them who retained sanity gathered their lunatic brethren and fled as they had come.

If he had known the effect the fungoids would have on them, he would have told them that too. He had told them everything else, when he had been snatched from a busy city street, a random specimen of humanity to be probed and investigated.

They had chosen well. For the payment they offered him he was willing to barter the whole human race. As far as it lay in his power he did just that.

He was not an educated man, though he was intelligent. It was child’s play to them to strip his mind bare; but they had to know the intangibles too, the determined will of humanity to survive, the probabilities of the pattern of human behavior in a situation which humanity had never before faced. He told them all he could, gladly and willingly. He would have descended to any treachery for the vast glittering reward they tempted him with.

It wasn’t easy for the Yugoslavs to guard him and, anyway, their hearts weren’t in the task. His treachery, the ultimate treason, the betrayal of the whole human race, was commonly known.

Inevitably the mob got him and killed three policemen in the process. When they had sated their anger a little and the traitor had lost most of his clothes and the thumb of his right hand, they dragged him to the junction where the Danube meets the Sava and held him under the gray waters with long poles, as if he was some poisonous reptile.

He lay supinely on the bed of the river and smiled evilly while a hundred thousand people writhed in neural agony.

Twenty-four hours later the neural plague had spread to Zagreb and into Albania as far as Tirana. When it crossed to Leghorn in Italy the Balkans held twenty million lunatics and the Danube was an artificial lake a hundred miles wide.

They had used a “clean” bomb. So they were able to bring a loudspeaker van to its edge and boom at him to come out. He allowed them to do that for some inscrutable reason; perhaps to demonstrate that his powers were selective. Then it seemed he got tired of the farce, and cruel fingers twined themselves into the nerve centers of the President of Italy and the Prime Minister of the government of United Europe. He made them dance a horribly twisted pas de deux on the banks of the Danube for his perverted amusement.

Then he released them, and released the millions of gibbering, twitching idiots that inhabited Southern Europe, and he came out of the river bed in which he had lain for forty-eight hours.

He walked alone through the deserted streets of Belgrade until he came to the United Nations building. There he told a very brave lieutenant that he was willing to stand trial any place in the world they wished.

For three days nobody came to arrest him. He sat alone with the lieutenant in the peopleless city of Belgrade and waited for his captors. They came then, timidly reassured by his non-violence. While he talked to them pleasantly the citizens of London and Paris suddenly began to dance jerky and grotesque jigs on the pavements of their cities. In the same moment the Chief Justice of the Court of the Nations, at a cocktail party in Washington, writhed in the exquisite pain of total muscle cramp, his august features twisted into a mask of abject fear.

The trial itself was a legal farce. The prisoner promptly pleaded guilty to the charge of betraying mankind to an alien race, but he didn’t allow them to question him. When one lawyer persisted in face of his pleasant refusals, he died suddenly in a cramped ball of screaming agony.