From the shard of stone and metal wherein a few desperate fugitives had taken refuge dropped tiny motes, tumbling hundreds of feet to certain, dreadful doom! Rocky could not hear their screams ... but he could imagine them. One of those black fragments _might_ have been ... _could_ have been.... He shook his head doggedly. No! He must not think of such things! Lynn still lived. _Must_ live! Then another sound burst so close to him that for a moment his tense nerves shrieked in agony. A mighty hissing roar ... the explosive blast of a rotor-gun going into action. Glancing to his right he found himself beside the very gun-embrasure wherein yesterday--("_Lord, only yesterday? Not a hundred thousand centuries ago?_")--a jovial gunner had told "Dr. Rockingham Roswell" fabulously genial tales of monstrous beasts. Could either of them have guessed that today.... "Gunner!" he cried. The old warrior glanced up, identified him amongst the hordes of refugees. "Oh, you, Puffessor! Come on! I'm short-handed here. Crew didn't make it afore the attack. If you're still lookin' for fab'lus monsters, here's y'r chance to git some fust-hand experience--" Rocky needed no second invitation. A terrible rage was upon him, now. Futile to attempt to any longer buck the mob to New Boston still more than three miles away. If Lynn had been in the city, neither he nor any man could help her now. The only thing he could do was ... avenge her.... He dropped into the pit, and swung instantly into action. "What do you need here? Oh--short a prime-loader, eh? All right, Gunner--" He spun toward the charge-rheo, jazzed its fill to max, slammed home the breech of the rotor, snapped, "O.Q. Charge set!" "Range," said Gunner mechanically, "_Fire!_" The beam blasted away. Then, and only then, did the old fighter seem to realize what had happened. His leathery old face crinkled, and he stared at Rocky in bewilderment. "Hey, wait a minute! What's goin' on here? Puffessor, where did _you_ ever learn to prime-load a Mallory rotor?" "The same place," grunted Rocky, "you saw a purple bird with six green wings and a lavender tail! Stop loafing! Let's give that beast another bellyful. Charge set!" "Range," said Gunner automatically, "_Fire!_" A slow grin overspread his face. "Comets! Looks like I pulled the wrong guy's leg, hey?" * * * * * But not long did Rocky work with the gun-crew. Came another buzz from Milligan, aloft. And this time the S.I.D. sergeant's news was worse than ever before. "It's no good, Rocky. Neither the groundfire nor our aerial blasts are having any effect on him. Heat-beams don't even make his muscles twitch, and as for physical ordnance--the shells don't even penetrate his hide." Rocky cried, "But there has to be some way to stop him, Bud! He's practically on top of New Boston now. After that, he'll turn on the Patrol Base--"