"She's telling the truth. I know all about that thing they sound off," he said breathlessly in his new, knowing voice. "When I was with Disbro--working for him--I had a look at it." "Stop your ears," Mara was bidding. "Quick! A rag from your garment will do!" She ripped away part of Planter's shirt, tore the piece in two, and thrust wads into his ears with her forefinger. Max was plugging his own ears. Then the sound began. When it began, nobody could say. Suddenly, it was there, filling space with itself as though it were a crushing solid thing. Planter, even with his ears partially muffled, almost collapsed. His body vibrated as before in every fiber, only not unendurably. He saw Max reel, but stay on his feet. Dr. Hommerson's men, a moment ago almost in the victor's position, were down, floundering in half-crazy agony. Planter understood, in that rear compartment of his mind that was always diagnosing strange things, even in the moment of worst danger. The Skygors were ill-cultured, poor of spirit, prospered chiefly by ideas stolen from the human beings they enslaved. But they understood sound waves, could use them roughly as an electrician might use electric vibrations. There were all the tales he had heard, of a chord on the organ that shattered window panes, of certain orators who could employ voice-frequencies to spellbind and impassion their audiences. This was something like that, only more so. Then he saw that Mara, who had thought of saving his ears, was down at his feet. "Mara!" he cried, though nobody could have heard him. He knelt, ripping away more rags of his shirt. He crammed them furiously into her ears. She stirred, got to her knees. She, too, could endure it now, and she smiled at him, drawnly. "I knew you would come back," her lips formed words. "David Planter--my David Planter--" Then she was up, crossbow at the ready. Because back came the Skygors, a wave of them in boats and as swimmers. Sure of their victory through sound, they were going to mop up the attackers. Max had a rifle. He lifted it, but on inspiration Planter leaped at him and gestured for him to hold fire. From beside one of the fallen Terrestrials he caught a grenade thrower. It was a simple amplification of an ordinary rifle. Upon the muzzle fitted a metal device like a bottomless bottle, the neck clamping tight to the barrel. Into the spread body of the bottle could be slid a cylindrical grenade, the size and shape of a condensed-milk tin. The grenade was pierced with a hole, and the gun, if fired, would send its bullet through that hole, while the gases of the exploding powder operated to hurl the grenade far and forcefully and accurately. * * * * *