"Because," answered Gary frankly, "there is something we need from your planet. We know, or believe, that the authors of this disaster threatening Earth dwell not in our solar system but beyond it. There is no spacecraft known to men capable of carrying us outside our own little solar galaxy. But if all human intelligence, the wit and wisdom of every planet, could be brought to contribute its portion, such a spacecraft could be built. It was our hope to gain the four requisite elements from the four major planets. The secret of the hypatomic drive from Earth; fuel from Venus; from Jupiter the secret of faster-than-light travel--" "And from Mars?" "From Mars," said Gary slowly, "a vital gift. Your most cherished defensive military secret ... the power shield. Yes, we know you have it, sir. We know it because--I am ashamed to say--you have been forced on several occasions to employ it against Earth's space-vessels. "Your science has discovered some form of force field which is impregnable against the onslaught of every known weapon. Our heaviest HE shells, our heat beams, needle rays, and rotor-blasts alike are harmlessly diverted by the magnificent barrier your people have invented. "With such a shield must the _Liberty_ be equipped if she is to dare a long and arduous trip through space to a hostile bourne. Not only is the entire journey made in peril of collision with rogue asteroids, bits of cosmic debris, and the like ... but when we reach our destination we will need protection against any conceivable weapon our enemy may bring against us. "Therefore, that for which we ask is a vital prerequisite to the safety and success of our journey." * * * * * Dr. Kang pondered briefly. Then, at length, "It is true," he admitted, "we possess a force-shield such as you have mentioned. But you have made one error. It is not altogether the defensive weapon you imagine it. It is, indeed, the reason your craft lies now on Deimos." "What?" interjected Hugh Warren. "You mean the intensified magnetization--" "Exactly, Captain. That is my reason for dwelling here on this outpost, twelve thousand miles from my beloved homeland. We of Mars have installed here a tremendous power plant capable of projecting its magnetic beam upon any vessel which approaches our planet. There is another similar station on Phobos. Master scientists control each of these laboratories. When spacecraft which we have reason to believe may have hostile intent approach Mars, switches are thrown converting these satellites into gigantic magnets of tremendous power. "That is why--" He smiled a bit ruefully--"That is why, on several occasions, Earth ships have crashed on Deimos and Phobos. Because it was clear they planned to disturb the quietude of our community." "But," cried Flick Muldoon, "how about us? _We_ didn't come here with a chip on our shoulders. _Our_ purpose was peaceful enough."