To find the murderer, it was of first importance to establish the background of this strange case. Access to the park is difficult--has been difficult ever since, more than a century ago, the area became a hunting-ground for thieves and hoodlums, and was transformed into a cultivated forest and garden preserved for aesthetic reasons, and to be viewed only from the mobilways above. (The boys who found the body are, of course, proof that the sealing-off of the park is not entirely effective--but surely only a daring and agile child could insinuate himself under the thorn-set hedges surrounding the park, or swing down to the tree-tops from the structure above.) If the victim had been killed elsewhere, how was her body carried to the spot where it was found? Both murderer and corpse would have had to penetrate unobserved into an almost impenetrable area. Could the body have been thrown from above? But if so, how could the remains of a full-grown girl have been transported from either a ground car or a copter on to the crowded mobilway, brightly lighted all night long? She must have gone there alive, either under duress or of her own accord. The first and most natural question, to Fedpol, was: who did have access to the park? The answer was, the gardeners. But the gardeners were out: they were all robots, even their supervisor. No robot is able to harm a human being. Moreover, no robot could have brought the victim in from outside if she had been killed elsewhere. The gardeners never leave the park, and they would repel any strange robot from elsewhere who tried to enter it. And one could hardly imagine a sane human being who would go to the park for a rendezvous with a robot! * * * * * It was Madolin's little sister, Margret, who interrupted the futile interrogation of the surly and resistant Pol Akkra and provided the first clue. She caught the eye of the investigating officer, Inspector Dugal Kazazian, and quietly went into the next room, where Kazazian followed her after posting his assistant with the father. "I promised Madolin I would never tell on her," she whispered, "but now she's--now it doesn't matter." She had loved her sister; her eyes were puffy from weeping. "She--she'd been going to Naturist get-togethers." Kazazian almost groaned aloud. He might have known--this was the first time they had been linked with murder, but it seemed to him that in almost every other affair he had investigated for the past few years, the subversive Naturists somehow had crept in. And if he had reflected, he would have suspected them already, since there seems to be no school or college which does not harbor an underground branch of these criminal lunatics.