Yes, but it was thunder caused by high voltage leaping across storm skies. It was the thunder of many powerful engines being revved up. Aircraft engines. And as Dawson leaned forward a little over the wheel and strained his ears, he knew in a flash that the thunder was from British and American-made aircraft engines. "They're revving them up!" he heard his own voice say. "Maybe the take-off's near. Must be, or they wouldn't show so much light. Yeah! They've removed the camouflage covering from the place, and that light is from runway flares, and maybe exhaust plumes. Dear heaven! Let us get through. Let us get through in time to do something. Don't let this terrible thing happen, please. I beg of you! Don't--!" Dawson's voice clogged up in his throat, and his heart seemed to shrivel into nothing as his own beseeching voice echoed back to mock him. And then, even as Freddy Farmer touched his arm, his straining eyes saw the second turn-off. There were three or four uniformed figures at the corner of the turn-off, and Dawson instantly tightened up inside. But there was no need of that A flashlight winked on, and its moving beam signalled for him to make the turn and keep going. Perhaps the car was recognized, but he doubted that because of the darkness. It was probably that any car that passed the first barrier down the road, and there had apparently been many of them tonight, was being allowed to continue on unchallenged to the secret field hidden behind the ring of hills. A great sigh of relief slid off Dawson's lips as he drove by the signalling flashlight beam and made the turn. A moment later, though, as he drove along a bumpy dirt road that led straight toward the ring of hills, his heart leaped up his throat to smack hard against his back teeth, and beads of nervous sweat stood out on his forehead. He heard Freddy groan softly, and that groan was echoed in his own heart. A short distance ahead he could see several cars parked off the dirt road. Several flashlight beams were moving about, and the road itself was blocked by several figures in uniform. In the bad light Dawson could not tell if all carried sub-machine guns, but he saw at least six, and to him that was six too many. No wonder his car had been allowed to turn off into the road leading to the secret field! "No cars allowed on the field, of course, because of the danger of fire," he muttered. "They're all being ordered to park outside, and those moving flashlight beams mean just one thing. That everybody is being checked before he can go the rest of the way on foot." He swallowed hard, and turned to young Farmer as the parked cars in front forced him to apply the brakes and slow down. "It's been nice knowing you, Freddy," he said in a dull voice. "This is the end of the line, and I mean the end. But I'm going to take some of the rats with me, that's certain!"