Signing off, Revere sent a, _Luck, Lynne--and Rolf. We’ll be here, standing by. Over and out._ They went back to Suzuki’s ship, lest further message sending cause another blast. There, Lynne telepathed Rolf, _Did you feel it--something else, something not alien?_ CREHUT, _now that you mention it._ Rolf turned to Suzuki, said, “Did any of your power instruments survive the blast, Lieutenant?” Suzuki looked at one of his technicians, a bearded, copper-skinned man called MacDougald. Macdougald scratched his head and said, “I don’t see how--unless the Sodium generator escaped. They buried it pretty deep. And they must have had it on. And once it’s on, nothing but a flip of the switch will turn it off for centuries.” “Why do you ask?” Suzuki wanted to know. Rolf and Lynne exchanged quick thoughts and Rolf said, “Because both of us received an impression that this element--this alien force--is suffering an unbearable irritation, which is amplified whenever any sort of power is turned on nearby. It’s--well, it reminds us of some sort of vegetable poisoning that can be stepped up to agony.” “We’ve got plenty of vegetable poisoning on Callisto, unlikely as it sounds,” said Suzuki. “The verdant stuff is latent all over the place. Goldberg nearly died of it.” He nodded toward a red-headed man whose forearms were swathed in plastibands. “The heat of our operations restored some of the stuff to virulence.” “Preventive shots no good?” Lynne asked sympathetically. Goldberg said, “They worked for the others, but not for me. It’s the worst itch I’ve ever had.” He winced. Rolf brought the conversation back on the beam. He said, “This element you’ve discovered is definitely superhuman mentally and emotionally. And it can and does kill when irritated. The picture we get is that here on Callisto it’s been left exposed on the surface and is sensitive to certain irritations. If your Sodium generator is an irritation, it’s got to be turned off before any of us can leave or any relief ship can land safely. Let me see a plan of the generator.” _What do you mean--here on Callisto?_ Lynne telepathed. _Do you think it exists anywhere else?_ _I don’t know--and don’t bother me_, was the reply, as Rolf bent over the blueprint MacDougald produced from a cupboard. He scanned it, scowling, then flashed a picture to Lynne, showing the generator, where it was buried, where the switch was that alone could turn it off. _Lynne, do you feel strong enough to try it?_ he asked silently.