The guess was correct. Before nine o'clock the ground humped into a range of foothills, and the darker masses of mountains could be seen behind them, rising up to obscure the stars.
"Stop the car here," Ulv said, "The caves begin not too far ahead. There may be magter watching or listening, so we must go quietly."
Brion followed the deep-cut grooves, carrying the radio. Ulv came and went on both sides, silently as a shadow, scouting for hidden watchers. As far as he could discover there were none.
By nine-thirty Brion realized they had deserted the sand car too soon. The tracks wound on and on, and seemed to have no end. They passed some caves which Ulv pointed out to him, but the tracks never stopped. Time was running out and the nightmare stumbling through the darkness continued.
"More caves ahead," Ulv said, "Go quietly."
They came cautiously to the crest of a hill, as they had done so many times already, and looked into the shallow valley beyond. Sand covered the valley floor, and the light of the setting moon shone over the tracks at a flat angle, marking them off sharply as lines of shadow. They ran straight across the sandy valley and disappeared into the dark mouth of a cave on the far side.
Sinking back behind the hilltop, Brion covered the pilot light with his hand and turned on the transmitter. Ulv stayed above him, staring at the opening of the cave.
"This is an important message," Brion whispered into the mike. "Please record." He repeated this for thirty seconds, glancing at his watch to make sure of the time, since the seconds of waiting stretched to minutes in his brain. Then, as clearly as possible without raising his voice above a whisper, he told of the discovery of the tracks and the cave.
"... The bombs may or may not be in here, but we are going in to find out. I'll leave my personal transmitter here with the broadcast power turned on, so you can home on its signal. That will give you a directional beacon to find the cave. I'm taking the other radio in—it has more power. If we can't get back to the entrance I'll try a signal from inside. I doubt if you will hear it because of the rock, but I'll try. End of transmission. Don't try to answer me because I have the receiver turned off. There are no earphones on this set and the speaker would be too loud here."
He switched off, held his thumb on the button for an instant, then flicked it back on.