"What?" asked Jack.
"Why, there"s a big level place just below the cave I was tellin" you "bout. A plateau. Smooth as a floor."
The hum of the airplane had died away. The boys and their guide never had caught sight of the machine in the darkness.
Suddenly Frank pointed in the direction whence the sound of the airplane had come, ahead and slightly to the left.
"I thought I saw a light there," he whispered. "It was just a faint streak of orange. Now it"s gone."
"Look here," said Bob to Tom Bodine, "does that cave face this way or is it on the other side of a hill?"
"It"s on t"other side," answered Tom, "an" near the top."
"Well, I"ll bet you there"s somebody in that cave. And the light that Frank saw was some kind of a signal to the airplane."
The big ex-cowboy scratched his head.
"Mebbe you"re right," he said doubtfully. "I don"t know "bout such things. But who"da thought that cave would be discovered. Why, I just come on it accidental like onct when I was wanderin" through these hills."
"Boys, there"s only one thing to do," said Jack in a determined voice, "and that"s to investigate."
"Righto, Jack," said Frank eagerly. "Here"s our chance to get back our airplane."
"You said it," declared Bob. "Let"s go."
"Not so fast," said Jack. "First we must have a plan of campaign.
Tom, what"s the lay of the land? How far away is the cave? Would it be better to leave our horses here and approach on foot?"
"Cave"s not more"n half a mile from here," answered Tom. "It"s just around the shoulder o" this hill we"re on right now and near the top.
I tole you "bout that big rock in front o" the entrance an" them three lonesome trees at the foot that give you a bee-line to the rock. Well, we can git to them trees without bein" noticed an" tie our horses there an" then sneak up afoot."
"Is there only the one entrance to the cave?"
"Only one," answered Tom. "There"s a kind o" chimney up through the rock to the top o" the hill. But n.o.body couldn"t git out there in much of a hurry. We won"t have to worry "bout that."
Frank had an idea.
"How far would those fellows in the airplane have to go to reach the cave after landing?"
"Oh, le"s see. "Bout as fur as us, I reckon."
"Maybe we can cut them off before they enter the cave," said Frank.
"They"ll be busy about the airplane for several minutes before they start to make their way to the cave. How would they have to approach the cave?"
"Same way as us from the trees on," said Tom.
"Well, if we hurry," Frank declared excitedly, "maybe we can capture them before they reach the cave."
"Right you are, young feller," approved Tom. "But we"ll have to leave our horses behind or they might give us away. We can"t tie "em to those trees like we planned."
"We can"t hobble them," said Jack, thinking quickly, "because they would wander aside a little distance, anyway. And we may want them again in a hurry."
"Tell you what," said Tom, "seems like I remember a clump o" trees just this side o" them three I spoke about. We can tie "em there. An"
them fellers in the machine won"t have no horses, so ours ain"t likely to nicker."
"Good," said Jack. "You lead the way and we"ll follow."
Presently at a low-spoken word from the guide the boys dismounted and tied up their horses. Then, Jack carrying his rifle, and the others following close at his heels, revolvers in hand, they pressed on toward the three trees forming Tom Bodine"s landmark.
As they reached the trees, low exclamations burst from the boys.
Hitherto, they had been cut off from the plateau by the shoulder of the hill. Now it lay below and before them. This of itself would not have permitted them to see, as the darkness was intense. But now the scene was illuminated by a number of oil flares stuck upright in the ground in a rude circle.
And right in the middle of the circle was the airplane stolen from Bob and Frank. There could be no mistaking the all-metal body nor the peculiar wing spread, even at that distance of close to half a mile.
Several figures were moving about. As the boys looked on, these seized oil flares and started moving toward them.
"Here"s where our turn comes at last," said Frank.
Jack laid a hand on his arm.
"Better than that, Frank," he said. "How many do you make out?"
"Three is my guess."
"The two men in the airplane and the man in charge of the cave," said Jack. "Dollars to doughnuts, the cave is undefended right this minute.
What do you say to capturing it and laying for them there?"
All four were grouped together, and consequently all heard Jack"s proposal. Bob and Tom Bodine agreed eagerly.
"Lead the way, then, Tom," said Jack, "because you know the route. And be quick."
Swiftly, yet withal cautiously, because the cave might be defended, they approached the big rock. As they sidled around it, a gleam of light from the mouth of the cave at the rear of the rock fell athwart their path. Involuntarily they drew back.
Then Jack brushed Tom Bodine aside and took the lead. His repeater thrust before him, crouching, he entered the mouth of the cave. A moment later his whisper came back:
"Coast"s clear."
But the others already were at his heels.
A hasty glance around revealed the first of the two chambers, which Tom had said the cave possessed, was luxuriously furnished and lighted by a powerful electric bulb enclosed in a huge frosted globe suspended from the middle of the roof. There was no time for further investigation because Jack already was pushing on toward the heavy hangings at the rear covering the mouth of the second chamber, and the others clung to his heels.
Parting the hangings quickly, Jack threw his rifle to his shoulder.
Then he and his companions received their second big surprise. The room was empty of human occupants. But it, too, was brilliantly lighted.
And it was a radio broadcasting station.
To the trained eyes of the boys that much was apparent at first glance. In one corner of the tremendous cave hummed the dynamo. From it, of course, came also the electricity for the lights. Before they could pursue their investigations, however, Tom Bodine, who had dropped back to the outer entrance, issued a warning hiss. Then he darted across the outer room and joined them.
"Three of "em," he whispered. "They"ll be here in a minute."