"Nay, for men rarely see them. For the most part, they do their evil deeds by night; and many are able to become invisible at their will. And some take divers forms: such are the werewolves, which are by day men, by night ravenous man-eating beasts." This was decidedly discouraging. I was still not sure, though, that de Long was not merely jesting. "Are these things likely to be dangerous to Martians?" I demanded. "I know not--but here in Engelond, as I have said before, there are much fewer of these fiends than elsewhere," he reassured me. I glanced nervously about the room. "Is it--is it possible that an invisible fiend might be present even here?" I knew that our scientists had produced invisibility in the laboratory, but it was hard to believe-- De Long nodded gravely. "Quite possible," he affirmed, adding sententiously, "Even walls have ears; speak of the Devil and his imps will appear." "Excuse me," I said falteringly. "I just remembered an important engagement--" I switched off the telepathor, gathered it up and made a hasty exit. I wanted to consult with Captain Tutwa. The captain listened with skepticism to my retelling of de Long's account of the dangers of the Blue Planet. "Bah!" he said, when I had finished. "The Earthman was probably lying, for some reason or other. These fellows have strange motives." "But why should he tell me such tales?" I persisted. "He seemed perfectly serious. And if such dangers _do_ exist on Earth--" "The motive becomes perfectly plain to me!" exclaimed the captain, snapping a tentacle in the air. "By telling us of imaginary dangers, the Earthman intends to frighten us away and preserve his sovereignty over the planet." "That sounds like a plausible reason," I admitted. "But--if he _is_ telling the truth, we are risking Martian lives every moment we remain here! We should at least check the facts." "Well...." The captain turned blue with concentration. "The Council, in chartering the Earth Expedition, expressed a fear that the planet might prove unavailable for colonization, due to possible inimical life forms. It's so much nearer the Sun, and so moist, that we had anticipated just such a canalbank jungle as does exist; and it's possible that the pressure of evolutionary competition might develop strange and fearful creatures.... But, remember that we haven't seen even one of these 'fiends.'" "De Long said that a great many of them are invisible." "Hmm!" said the captain. "Of course, that's within the bounds of possibility, though not of probability; but before we came here I'd have said flying animals were improbable. We had best investigate." "Eh?" "It's simple. We'll merely put de Long under the lie detector." * * * * * I was struck by the beautiful simplicity of this idea, which should have been right in my province. "I leave it to you to maneuver de Long into a position where we can use the detector without his knowledge," said the captain.