The sun rose higher and higher, a dim, small, feeble-looking sun, glowering out of a cloudless purple sky.
Tuck’s eyes were smarting from the staring, but he kept the binoculars tight to his pressure helmet. An hour passed as they moved slowly out from the colony in ever-widening circles. Finally he dropped the binoculars disgustedly. “I wouldn’t see anything if it walked up and kicked me,” he growled. “All I see is gorges and cuts and cliffs—”
“Want to let me look for a while?”
“And let me fly?” Tuck’s heart leaped.
“Think you can do it?”
“Of course. I won’t go as low as you are, but I can almost match it.” He held on as David slid into a long, even stretch, then rose higher and shifted the controls to automatic. The cockpit was a tight squeeze, but they managed to shift, and in a few moments Tuck’s hands were gripping the semicircular wheel, and he felt the little scooter responding to every touch, every movement. He brought the ship up in a high arc, exhilaration shooting through him to the depths of his bones. His mind went back for a second to the obstacle races he had flown back in school; then he brought the ship in low. He found the place where they had left their circles, and closed in, picking up a landmark in each quarter turn every time around, moving slowly outward. The colony grew farther and farther away as the minutes lengthened into another hour, and his hopes dwindled with every minute—“Wait—” David stared into the binoculars, shifting around as the ship left the ground behind. “Wait a minute—”
“See something?”
David scowled. “Can’t tell. Bring her in very low, right over that stretch there—see the gorge running off at two o’clock? Try to follow it” His voice was excited, and he peered down, holding the binoculars ready. Tuck swung the ship around and brought her in, scooping down as low as he dared. He could pay no attention to anything but the path the ship was taking, and he saw the walls of the gorge rise up on either side as they skimmed through. And then David let out a yip of glee. “Here,” he cried. “Let me take it. See what you see! Just this side of the gorge, over to the right—”
Tuck relinquished the controls, peered through the binoculars at the jagged ground below. At first he could see nothing; then, as they swooped over, he saw what looked like a deep, black, perfectly rectangular hole—
“Looks like a cave-in!” He cried.
“Looks like it.”
“Is this the one you saw?”
“Nope. This is lots farther out.”
“Think we can get into it?”
“We can sure try!” He slid the ship down, searching for a smooth place to land. “At any rate, we’ll take a look. This may be our way into the tunnels.” He was busy at the controls for a few moments, and then the ship was down, and the sound of the jet was dying away in their ears. In a moment they were out, lumbering for the fault as fast as their clumsy suits would let them—
The hole was about thirty feet deep, perfectly rectangular at the top, but sloping up from the bottom on one side, as though one section of the tunnel had given way, and a landslide piled into it. As they stared, they could see at the bottom an opening, leading into a black hole that seemed to disappear into the wall of rock.
“It is a tunnel!” David was scrambling down the side, staring at the other side of the hole. Tuck hesitated.
“Seems odd there isn’t an alarm, if it goes into the tunnels—”
David shook his head. “Not so strange. The colony end of the tunnel is completely blocked off by the cave-in. This must open into the outer end.”
Tuck peered down at him. “You think it’s cut off from the main tunnel back to the colony?”
David nodded. “And look there—” He pointed to a large chunk of smoothly scooped-out rock lying in the debris. “Looks like we can thank our little silicon friend for this, too. Probably this cave-in is quite recent—”
“Shall we go in?”
“Might as well—even if it is a dead end.” David climbed down to the bottom of the slide, cleared rocks away from the black hole, and stuck his head in. A moment later he looked back. “Come on. This goes quite a way in.”
Tuck clambered down, careful not to cut his pressure suit on the jagged rocks. Together they struggled through the tunnel, snapping on their helmet lamps as the darkness closed in on them. The tunnel was seven or eight feet high, and four feet wide, beamed heavily on the sides and overhead. Thirty yards ahead it curved to the left and disappeared into the darkness—
David stopped after a few steps, and turned to Tuck, a strange expression in his eyes. “Wait a minute,” he said softly.
“What’s wrong?” Tuck’s voice was a startled whisper.
“Everything!” David whispered back. “I’ve been thinking. I don’t remember any tunnel here. No tunnel of any sort. I’ve studied all the maps, and the maps say that there’s a large vein of radioactives between here and the colony—and no way to dig through it safely—”
Tuck’s eyes widened. “This is a tunnel, map or no map—” He stopped short, staring over his shoulder at the little patch of light, then back at David. “You mean—”
“Has your Geiger been acting up since we came in here?”
“Not a peep.”
“That’s what I thought. There’s a tunnel through here, all right, but not through any radioactive vein, and not on any map that I’ve ever seen!” He jerked his head and started down the tunnel. “Buddy, we’re on to something!”
They plodded on in silence. The stillness of the place was oppressive, almost ghostly; their footsteps echoed and re-echoed in the darkness. As the tunnel curved, the opening to the outside disappeared, and they were in total darkness except for the flicker of their helmet lamps.
“Look!” said David suddenly.
Forty feet ahead the tunnel suddenly broke into a Y. One branch curved gently off to the left, and then down. The other cut sharply to the right. And at the junction was a large, dull metal object.
Tuck stopped short and stared. “What is it?”
“A pump and blower. There have been cave-ins before in this tunnel—and that means it’s an old one. And look at the beaming—wooden! They haven’t beamed tunnels with wood for years.”
“Let’s split up here,” said Tuck. “I’ll take the right, you take the left. Will the phones carry through this rock?”
“For a little way.”
“All right. Look—let’s each walk for ten minutes. Then come back. Meet me here in twenty minutes.”
“That’s good,” said David. “There’s something about this I don’t like.”
Tuck waved and started down the right-hand tunnel. It cut very sharply around, then suddenly straightened. Tuck walked slowly, the only sound those of his own footsteps. He shivered, suddenly, as he walked. A tunnel where there was no tunnel on the map—beyond a radioactive bed that didn’t exist. His heart pounded wildly. It could be only one thing. But what if they were caught down here, snooping into some strange underground vault that had been kept deadly secret for a century—what could they do? Tuck realized with a jolt that he hadn’t thought of weapons. With the tunnel open to the outside, a quick blow to smash his helmet would be the end—
The tunnel widened suddenly, and he was in a small room, packed to the ceiling with sandbags. And against one wall were boxes—he peered at them, curiously. They were aluminum cargo boxes, stacked one on top of another. Every box had a stencil on its side that read, “Titan Colony, via Rocket Freight.” followed by a date—
“Tuck!”