Stark smiled. He leaned over and kissed her. "I'll be careful, little sister."
Quite suddenly she flung her arms around his neck and clung to him tightly, and Stark's face sobered. He patted her, rather awkwardly, and then she had gone, to curl up on her own pallet with her head buried in her arms.
Stark lay down. His heart was sad, and there was a stinging moisture in his eyes.
The red eternities dragged on. Stark learned what Helvi had meant when he said that the mind broke before the body. The sea-bottom was no place for creatures of the upper air. He learned also the meaning of the metal collars, and the manner of Tobal's death.
Helvi explained.
"There are boundaries laid down. Within them we may range, if we have the strength and the desire after work. Beyond them we may not go. And there is no chance of escape by breaking through the barrier. How this is done I do not understand, but it is so, and the collars are the key to it.
"When a slave approaches the barrier the collar brightens as though with fire, and the slave falls. I have tried this myself, and I know. Half-paralyzed, you may still crawl back to safety. But if you are mad, as Tobal was, and charge the barrier strongly...."
He made a cutting motion with his hands.
Stark nodded. He did not attempt to explain electricity or electronic vibrations to Helvi, but it seemed plain enough that the force with which the Lhari kept their slaves in check was something of the sort. The collars acted as conductors, perhaps for the same type of beam that was generated in the hand-weapons. When the metal broke the invisible boundary line it triggered off a force-beam from the central power station, in the manner of the obedient electric eye that opens doors and rings alarm bells. First a warning—then death.