CHAPTER V.--THE REVELATION OF A TRAGEDY.

"Smugglers!" Frank exclaimed, dropping an armful of unopened opium tins on the floor of the cavern. "Smugglers, all right, all right!"

Ned looked the tins over carefully. They were well covered with Chinese characters, and were dirty, as if they had been hidden away in the earth for a long time.

"Who would have suspected it?" Frank continued. "We are close to the British frontier, but, all the same, this seems to me to be an awkward place to land and store the dope stuff."

"Where did you find it?" asked Ned.

"There is a false back to that cupboard in the north wall," Frank replied. "When I knocked on the boards they gave forth a hollow sound, and so I tore one away. Hence the opium. And there are pipes there, too--just such pipes as one sees in the joints on Pell street, in little old New York."

"You remember what Jimmie said?" asked Ned.

"I remember a good many things the little rascal has said," was the laughing reply. "He's always saying something."

"Well," Ned continued, "the boy was right when he expressed his opinion of the heelless footprints in one word."

"Chinks!" grinned Frank. "Of course!"

The boys now went over to the cupboard in the niche and began tearing away the boards. After a few had been displaced Ned stopped and began experimenting in fitting them in position again.

"What's doing now?" demanded Frank.

"We must remove them so as to be able to return them as we found them before we leave," Ned replied. "It is important that the inhabitants of this robber den do not know that we have discovered it."

"Don't you ever think they don't know it right now," Frank said. "We haven't seen any of them since they rowed around the point, but they're stirring about, just the same. We may see more of them before we get out of this cavern."

"Well," Ned said, "we must take all the precautions needful, and if they are of no avail we shall not be to blame for what takes place. Even if they know that we have found the cavern, they need not know that we have penetrated into the office chamber. Now, draw that last board away carefully, and we'll see what there is behind the false bottom."

Frank drew the board away and was confronted by a long, low tunnel--an uncanny, narrow tunnel which had evidently been enlarged from a fault in the rock, and which appeared to penetrate far into the bulk of the mountain.

"See!" he cried. "The cupboard was built at the mouth of a cross fault in the rock, and there is no knowing what is behind it. Hold your flashlight higher and I'll crawl in and look about."

"Be careful," Ned warned. "I have seen great holes at the bottom of tunnels like that. Don't break your neck, or tumble down so far that I can't fish you out."

Frank grinned and crept through the opening made by the removal of the back of the closet. The place was not high enough for him to stand upright, and so he proceeded on hands and knees.

"This is a bedroom," he shouted back to Ned. "There's lots of ticks and blankets here."

There was silence for a moment, and then the boy's voice came from farther in the tunnel. "And here's kegs of whisky," he cried. "It smells like a Bowery saloon. Come on in!"

"I think one of us would better remain outside," Ned replied. "I wouldn't like to be surprised while in there and fastened in with rocks."

Frank went on down the tunnel for some distance, calling back, now and then, to report his discoveries. There were weapons stored there, barrels of gasoline, packages of dynamite.

Then, for several long minutes, there came no voice from the interior, and Ned put his head inside and called out softly:

"Frank!"

There was no reply, and Ned was about to advance into the opening when the sound of a footstep came on the rocky floor of the chamber just behind him. The footstep was a stealthy one, halting, as if some person were listening between the steps. Ned's first act was to shut the light off from his electric candle.

Then he moved away from the niche in the wall where the cupboard had been built in and waited. His greatest fear was that Frank would turn about and show his light, and so expose them both to danger. While he listened, almost holding his breath, the steps came nearer to the cupboard and halted.

But the halt was only for an instant, for the unseen figure moved on again, this time back toward the entrance. Directly the footsteps were heard no more, and then the crash of falling rocks reached the boy's ears. He did not have to think long in order to understand what that sound portended.

He knew that they had been observed by some of the outlaws who made the cavern their home and their storehouse as well, had been followed into the inner chamber, and were now to be fastened into the cavern, probably left there to starve, with tons of rock bulking before the entrance to the third chamber. It was not a pleasant situation.

While he studied the peril over in as optimistic a mood as was possible under the circumstances, he heard Frank calling to him from the narrow tunnel behind the cupboard. The boy was evidently excited, for his voice rang high.

"Ned!" he cried. "Come on in!"

The noise of falling, rolling rocks stopped at the sound of Frank's voice, and Ned thought he heard a half-suppressed chuckle in the darkness.

"Hurry!" came Frank's voice once more. "There's something in here that takes the nerve out of me."

There was a low exclamation of rage at the entrance, where the stones were piling up, and then the grind of falling rocks was continued. Ned had, of course, no idea as to how many persons were engaged in building up the wall which threatened to shut him in until life was extinct, or exactly how it was being done, but he knew that the correct thing for him to do was to prevent the completion of the work.

If only one man had arrived at the cavern he might be frightened and driven away by a little shooting. With bullets whizzing through what was left of the opening, the man who was building the crude wall would not be likely to present his body before the space still uncovered. This reasoning brought the boy to a consideration of the matter of ammunition, but he decided that, with the cartridges carried by Frank, they could defend the place for a long time.

But another question intervened. The rocks which, though unseen, he knew to be blocking the space where the rug had hung were undoubtedly falling from a distance. They might have been stored above the natural doorway for the very purpose to which they were now being put.

If this were true, then the building of the trap would continue, regardless of his bullets. While he studied over this problem, slowly making up his mind to put it to the test, Frank's voice came from the tunnel again.

"What's doing out there?" the boy asked. "Why don't you come in here?"

"Shut off your light!" ordered Ned, as a glimmer showed inside.

"Not me," replied Frank. "I need all the light I can get in here!"

"What have you found?" asked Ned anxiously.

Frank did not reply instantly, and Ned heard the rattle of stones while he waited for his answer. The task of piling up the wall was progressing rapidly, and it seemed to the boy that the stones were all falling from a distance.

"Shut off your light and come out," Ned said, impatient at the hesitation.

"I wouldn't stay here in the dark for a thousand dollars a second," Frank replied, "but I'll come out. Why don't you show a light?"

"I'm not looking for any chance bullets," Ned replied, coolly. "We're caught, my boy, and it is up to us to move cautiously. Why don't you turn off your light?" he added, half angrily.

"Oh," Frank replied, "you're getting it out there, too, are you? Well, I was trying to save you a shock. There's a dead man in here, and I'm going to keep my light going until I'm out of the hole. I did shut it off once, and felt the grasp of a hand on my neck--and there wasn't any hand there either."

"A dead man?" repeated Ned.

"Sure," Frank replied. "And he's not been dead very long, at that."

Again the boy heard that vicious chuckle at the entrance. Then a voice came out of the mouldy darkness:

"How are you getting on in the Secret Service, Ned Nestor?" the voice asked.

"Finely!" Ned called back, but it seemed to him that his voice shook with the peril of the situation. He was known, his mission there was no secret, the enemies of the government were already on the ground, ready to combat him in his work. Just how far their hostility would extend was evidenced by the fall of rocks outside. It seemed to the boy that the struggle would be to the death.

"Who are you talking to?" Frank asked.

Ned did not reply to the question, for there came the sound of a scuffle outside, then a shot, a cry of pain, and the cavern was still as a grave.

In the silence Frank's movements were heard, and Ned knew that he was backing out of the tunnel, with his light still burning. Entirely at a loss to account for the fracas outside, Ned awaited his approach with a fast-beating heart. When at last he shut off his electric searchlight and dropped from the tunnel through the old cupboard Ned seized his hand and drew him away.

"Did you fire that shot?" Frank whispered.

"No," was the reply. "There's fighting outside, and the shot was fired there. Now, I had a notion of sending a stream of bullets through the doorway, but the persons who are fighting the man who came upon us here may be our friends, so we must be careful what we do. Here. Take my flashlight. Open the two at the same instant and turn the rays on the doorway. I'll be ready with my gun."

But before this movement could be carried out a voice the boys knew came out of the darkness.

"Wonder you wouldn't give a fellow a lift," Jimmie said, in a panting tone. "I've got to the limit with this big stiff."

The lights were on instantly, with Ned and Frank bounding toward the opening. The way was narrow, for many rocks had been dropped down from a broad ledge just above, but they managed to crawl through. But before Ned could reach the struggling pair on the floor the under figure wiggled away, staggered for an instant, and then made for the outer air at good speed.

Jimmie sat upon the stone floor with a disgusted look on his freckled face.

"Now see what you've been an' gone an' done!" he cried. "You've let me pirate get away! But he took a bullet with him," he added.

"How many were here?" asked Ned, shutting off his light and telling Frank to do the same. "How many men did you see?"

"Just that one," Jimmie replied, sorrowfully, "an' he got away!"

Ned advanced to the entrance and listened. At first he heard the sound of limping footsteps, then the sweep of oars. He ran down to the beach and swept his light over the waters of the lake. A slender boat was speeding far to the north, and a solitary rower was bending to his work.

Now, for the first time, Ned noted that a fierce gale was blowing from the west, and his thoughts went back to the plateau where the aeroplane lay exposed to the storm. He ran back to the cavern, barely escaping being blown off his feet on the way, and called to the boys.

"There's a stiff wind blowing," he said, "and I'm afraid for the aeroplane. We must get back to the camp immediately."

"The wind was on when I came in," Jimmie said, "an' it near blew me into the lake, even if I did hold on to the trees. We can never make the hill in the storm."

"We've got to," Ned insisted.

"Besides," Jimmie continued, "we want to find out about the dead man Frank has been telling me about. We can't take him with us, an' he will not be here when we come back. Whatever we learn about him, an' the cause of his death, must be learned now."

"Sometimes, Jimmie," Frank burst out, "you exhibit signs of almost human intelligence!"

"The boy is right," Ned observed. "I'm so rattled that I hardly know what I'm about. We ought to be in pursuit of that rascal who is rowing on the lake, we ought to be on the plateau, looking after the aeroplane, and we ought to be here, finding out if a murder has been committed."

"It is a murder, all right," Frank said, "for the floor in the tunnel is sticky with blood."

"I'm goin' in there!" Jimmie exclaimed.

"Go if you want to," Frank grunted.

Ned laid a hand on Jimmie's arm as he started away.

"If you don't mind," he said, "I'd much rather you remained on guard. You have keen eyes, and may be of great service here."

"All right!" the boy said. "I'll do anything you ask me to if you don't leave me out of the game."

"No danger of your getting into the dust heap," Frank laughed. "How long have you been prowling about here?"

"Just a short time," was the reply. "I remained in the tent until I thought Pat an' Jack were asleep an' then cut my lucky. Say, but the wind was blowin' when I slid down the slope toward the lake."

"It must be fierce up on the plateau," Frank admitted. "Say," he added, turning to Ned, "if you don't mind, I'll go on up the hill and help the boys with the aeroplane. It would be a tragedy if it should be destroyed now."

"All right," Ned said. "Get up there as soon as possible. The boys may be having trouble with the 'plane. And Jimmie," he added, "suppose you keep an eye on the plateau? The lads may signal."

"Too dark for that," the boy replied, "but I'll keep a sharp lookout, just the same. Go on and look over the man Frank found under the mountain."

Frank moved on up the hill, clinging to trees as he advanced, and stooping low, even then, to escape the force of the wind, while Jimmie stationed himself in the opening and looked out on the lake. Ned disappeared in the cavern, and the boy saw his torch grow fainter as he climbed through the narrow opening left in the rock which had been thrown over the natural doorway.

It was getting late and the boy was sleepy, but he struggled manfully to keep his eyes open. Directly, however, he had no trouble in this regard, for he started up with a strange, acrid odor in his nostrils. The low-lying sky was aflame.