At daybreak Frank Shaw stood in the screened porch facing west, watching and waiting for the return of Nestor and Jimmie. It had been a long night for him, but he had kept his vigil alone, knowing that his chums needed all the rest they could get.

Many times between midnight and morning the noises of the tropical forest had taken on the semblance of human voices, and then he had crept out from the screens to listen intently for some indication of the approach of his friends. But they had not come, and now he was anxious to set out in search of them.

While he stood there with his brain filled with forebodings of evil, he heard a step in the cottage, and then Jack Bosworth stood by his side, bright and exuberant of spirit after his long sleep. He stood silent for a moment, looking out into the wonderful jungle and then turned to Frank.

“Great country,” he exclaimed, sweeping a hand toward the gorgeous thickets.

“A dangerous country,” Frank said.

“And a country for an appetite,” cried Jack. “I’ll get the boys up and we’ll have breakfast. Why,” he added, turning back to the porch after glancing over the row of bunks, “where’s Ned?”

“He went away at midnight,” was the reply, “and hasn’t returned. I’m afraid something serious has happened to him.”

“And you have been watching for him all night?” asked Jack. “Why didn’t you waken me? I reckon I’m entitled to a fair share of what’s going on here, be it good or bad.”

Frank told the story of the night briefly and Jack listened with a frown on his brow. His fingers clenched at mention of the bomb which had been placed under the floor of the cottage.

“We’re spotted, of course,” he said, when Frank concluded the story. “If we had only tipped His Nobbs off the ship on the way over.”

“I suggested that to Ned,” Frank answered, “but he only laughed at me. He declared the fellow to be the missing link between himself and the principals in the Gatun dam plot.”

“What’s the answer?” demanded Jack, with a puzzled air.

“Why, it is his theory that half of the criminals of the world would escape punishment if they could only learn to lie quiet until they were looked up.”

“I see. His notion was that the plotters, guided by His Nobbs, would visit us with hostile intentions, and that they might leave a trail back to their own camp.”

“That is about it.”

“Well, they seem to have looked us up all right.”

The other boys now came tumbling out of the cottage, shouting their greetings to Frank and Jack and the golden morning, and clamoring for breakfast. Five minutes later, when the events of the night had been explained, their healthy appetites had vanished. Even when the cook began preparations for the morning meal, filling the air with tantalizing odors of cooking food, they sat in serious consultation with no thought of breakfast in their minds.

“What ought we to do?” asked Jack.

“Go and look him up,” suggested George Tolford.

“He may have become lost in the jungle,” Peter Fenton remarked. “Suppose we go out into the jungle and fire our guns?”

“I’m afraid it is worse than that,” Glen Howard remarked. “We ought to let Lieutenant Gordon know about it.”

“I am afraid Ned wouldn’t like that,” Frank said.

While the boys discussed ways and means a dusky youth of perhaps twenty was seen approaching the cottage on a run. His dress was half American and half native, but his face was wholly Spanish. He paused when he discovered the boys on the porch and held out his hands, as if to show that his mission was a peaceful one. Frank motioned to him to approach and opened the screened porch door for him to enter.

“Good-morning, gentlemen,” he said, in excellent English. “I am from Lieutenant Gordon.”

“Then I think you’re the fellow we are looking for,” Jack said.

“He wants you to join him up at the Culebra cut,” the youngster continued. “The two who left the cottage last night are there waiting for you.”

“Glory be!” shouted Jack. “We were just wondering what had become of them.”

“They wandered out to Gatun and came upon the lieutenant,” said the messenger.

“In the night?” asked Peter, suspiciously.

“A little while before daybreak,” was the ready reply.

“We’ll go and get ready for the journey,” Frank said, but at the door he beckoned to Jack and they walked away together.

“What do you think of him?” asked Frank.

“Why, he seems to be all right,” was the reply. “At any rate he knows about the boys going away in the night and not coming back.”

“The man they followed away would know that, too,” Frank said.

Jack looked his friend in the face for a moment and scratched his head.

“Say,” he asked, “do you think this is a stall?”

“I don’t like the looks of the fellow,” was the reply. “Besides, what would the boys be doing up at the Culebra cut?”

“If you think it is crooked we won’t go,” Jack observed.

“Another thing,” Frank went on, “we were to have nothing to do with Lieutenant Gordon while on the Isthmus. We were to roam about at our own sweet will and pick up what information we could. So it doesn’t seem likely that he would send for us all to meet him at the Culebra cut. Does it, now?”

“No, it doesn’t look reasonable,” Jack admitted.

“You know what we were saying about Ned’s theory?” Frank asked, in a moment.

“You mean our talk about criminals pointing the way to their own destruction by unwise activity in defensive methods? Of course I remember it. If what we suspect is true, though, Ned rather overplayed it in this case, and got caught.”

“We don’t know yet whether he got caught or not. We only know that he is unaccountably missing. Well, what if we accept Ned’s theory here and go with this messenger? If he is on the square he’ll take us to Ned. If he is crooked he’ll take us to people who know why Ned did not return to the cottage.”

“It may be easier to get taken to the people you speak of than to get away from them,” Jack said, dubiously.

“I’m game to try it, anyway,” Frank continued, “but I think we ought to leave one behind at the cottage, for Ned may return, possibly, though I doubt it. Anyway, it will do no harm to leave some one here.”

“Suppose,” suggested Jack, “we don’t leave any one at the cottage, but instruct one of the boys to remain here when we go with this fellow and then follow on immediately, sort of keep track of where we are taken?”

“That’s a fine idea,” Frank replied. “I’ll go with the messenger and take the boys with me. You remain here and see where we go – that is, you remain here when we leave and then trail on after us, like a Sherlock Holmes.”

“I would rather go with you,” Jack replied, “but I’ll do the sleuth act if you prefer to have me. You’ll need a rescuer, all right,” he added, “for Lieutenant Gordon never sent that chap after us. Never in the world.”

The cook soon called the boys to breakfast, but there was not much eaten, greatly to the disgust of the cook. When they left the table the messenger asked if they were ready to go.

“All ready,” cried Frank, but Jack threw himself into a chair and took up a magazine, watching the face of the messenger over the pages as he did so.

“You are to give up the cottage,” the messenger said, with a frown of disapproval. “No one is to be left here.”

“It will be all right for me to remain here until the others come,” Jack said, with a smile. “I don’t feel like a walk this morning.”

“There is a motor car just over the hill.”

“No inducement,” laughed Jack. “I’m going to remain here.”

The messenger said no more, though it was plain that the arrangement did not please him. In a few moments the boys were off, the messenger leading the way and keeping up a running fire of conversation.

“What do you think of that?” asked Jack of the cook, as the party disappeared in the thicket.

“I don’t like it,” was the reply. “I overheard what Frank told you about the disappearance of Ned and Jimmie, and was anticipating something of the kind.”

“Why didn’t you say something?”

“It was not for me to interfere,” was the reply.

The cook, known as Tommy, was looked over critically by Jack.

“I believe you’re all to the good,” he said. “You wouldn’t be here if you wasn’t. Now, what do you say to exchanging clothes with me?”

“I have no objections, only I don’t exactly see – ”

“We’re just about the same size,” Jack went on. “Same black hair and black eyes, same ugly smooth face – glad you have no whiskers. You’re tanned up a little, but I can put some stain on my face. There you are. The cook goes to Gatun and Culebra and Jack Bosworth remains at the cottage. They won’t think of molesting the cook.”

“I would rather go with you.”

“But some one ought to remain here,” urged Jack.

Tommy thought over the proposition for a moment and smiled.

“All right,” he said. “I’ll remain here, as long as necessary,” he added.

The exchange of clothing was quickly made and Jack managed to darken his face with a stain made of crushed leaves which Tommy gathered for him.

“Now, you’ll stay right here, won’t you?” Jack asked, as he passed out of the doorway. “Ned and Jimmie may return, you know.”

“Yes, I’ll stay right here,” the cook said with a grin.

But as Jack entered the thicket he added:

“Until you get out of sight. Then it is me for the Tivoli and Lieutenant Gordon. It looks to me as if these babes in the woods had bitten off more than they can chew.”

Whether his supposition was right or wrong, the cottage was closed in five minutes, and Tommy, wearing Jack’s clothing, was racing through the path Ned had taken the night before, on his way to Lieutenant Gordon.

His journey on foot, however, was destined to be a short one, for at the turn of the path he came upon a man loitering in the open space just ahead.

“Wait a second,” the man exclaimed.

Tommy was not inclined to check his pace, but a revolver in the hands of the fellow induced him to do so.

“You are Jack Bosworth?”

Tommy hesitated. For an instant he thought of declaring his identity and so getting away to the Tivoli and Lieutenant Gordon. The man in his path settled the problem for him.

“No use to deny it,” he said. “You are to come with me.”

“Where?” asked Tommy.

“If you have any weapons give them to me,” the other said, gruffly, paying no attention to the question.

“All right,” Tommy said, handing out a revolver. “It is a heavy thing to carry, anyway. Where are you going to take me?”

“Straight ahead,” cried the captor, with a frown. “Straight ahead. I’ll tell you when to turn and when to stop.”

“You seem to have an accommodating disposition,” laughed Tommy. “Why didn’t you stop the cook, who went out a little while ago? Perhaps he would have been glad of your company.”

“We are not interested in the cook,” came the answer, and Tommy smiled as he thought that at least one point of the ruse had met with success.

“That cook will be fired for leaving the cottage,” grinned Tommy, making the deception as complete as possible.

In the meantime the motor car containing the five boys and the messenger was speeding on its way toward Gatun and the Culebra cut. When Jack came out on the road the machine was disappearing from sight, but he managed to keep track of it from the hilltops for a considerable distance.

The messenger was full of talk, his evident intention being to keep the boys interested. In spite of the attention paid them, however, Frank and Harry Stevens managed to hold a conversation on the back seat.

“This is carrying out Ned’s theory with a vengeance,” Harry remarked. “If we get dumped into the big cut we’ll charge it up to him.”

“The play opens with plenty of action in the first scene,” grinned Frank.

“The adventure would look better to me if I knew what had become of Ned and Jimmie,” Harry said, despondently.

“If we keep up the appearance of being pleased with the ride,” Frank said, “we may be able to learn something of their whereabouts. It is mystery to me how the plotters got hold of Ned, if they did get hold of him.”

“You recall the talk in New York as to whether the men who entered Mr. Shaw’s study were in quest of the plot papers or the emerald necklace?” asked Harry.

“Yes; and I’ve been studying over that problem ever since.”

“Well, I’ve been wondering, ever since we started out on this rather risky trip with the messenger, whether the people Ned encountered last night, and the people we are likely to meet to-day, are the people of the plot papers or the people of the emerald necklace. What do you think about it?”

“I fail to see why the necklace thieves should bother. They’ve got the trinket they wanted, haven’t they? It is the canal blowers we are facing now.”

“You know Ned’s theory,” whispered Harry. “Well, if the necklace thieves have brought the bauble back to the Isthmus, they think we’re hot after them, and so may strike at us before we can get our guard up. See?”

“No, I don’t see,” replied Frank. “I’d like to believe they brought the necklace over here, though. Then I might stand a chance to get it back. You’ll find that it is the men who are plotting against the big dam that we are mixing with.”

The motor car ran through Gatun without stopping, and finally drew up at a rambling old structure which seemed to have been deserted ever since the days of Balboa. The messenger explained that they were to wait there for the lieutenant, and all entered the ancient ruin, the boys looking carefully about as they stepped through the doorway.

The room which first received them was long and narrow, with walls showing both age and neglect. They were met at the door by a tall gentleman of military bearing and a dwarf whose mischievous black eyes stared fixedly into their faces.

“The lieutenant is late,” the military man explained. “If one of you is Frank Shaw, however, a portion of the business of the day may be taken up before his arrival.”

Frank admitted his identity, and was invited into a smaller room opening from the apartment in which the others waited.

CHAPTER VIII.
EXPLOSIVES FOR THE GATUN DAM

Ned and Jimmie listened for some moments to the steady click-click of metal which came, or appeared to come, from the ground directly underneath their feet, and then Ned arose and crept forward.

“Where you goin’?” whispered Jimmie.

“Down there.”

Ned pointed to the dark corner.

“You’d better come away,” warned the boy.

“We are here to investigate,” Ned replied, almost impatiently.

“Then investigate with a bomb, or with a cannon,” advised Jimmie.

“No time for that,” came the reply. “The conditions which exist now may not exist in an hour’s time. It is now or never.”

Moving forward, Ned saw a faint finger of light cutting the shadows in the corner Jimmie had pointed out. Jimmie saw it at the same instant.

“I’ll bet they’ve got a blacksmith shop down there,” he said.

There was no opening in the great stone slabs of the floor through which a man might make his way – only the crevice through which the ray of light came. Ned turned his attention to the wall to the south.

Behind a luxuriant growth of vines he saw another glimmer of light, and in a moment stood looking down a narrow stairway, at the distant end of which were numerous lines of red flame. Jimmie, looking over Ned’s shoulder, uttered a muffled exclamation.

“Looks like a door made out of red-hot bars,” he said.

“It is a board door,” Ned whispered back, “with wide cracks between the planks. There is an intense red fire in the room beyond.”

Ned placed a foot on the top step of the stairway and slowly and cautiously rested the weight of his body upon it, to make certain that no trap for the protection of the place had been set there. The stone step was solid and bore his weight firmly.

At the bottom of the stairway the boys stopped and looked about. Straight ahead was the cracked door, to the south was a solid wall, to the north, under the stone pavement they had crossed to gain the corner, was a dark room, the door to which stood open. The room was close and hot.

“How are your matches, Jimmie?” whispered Ned.

“Got a pocketful,” was the reply. “Want a light?”

“Not yet. We would better feel our way into the room. Keep close to me and keep your gun handy.”

The room was small, something like a vestibule to a larger one which ran along parallel with the one from which the light came. It was very dark there, and more than once the boys stumbled over obstructions on the floor, which seemed to be of brick or stone. Once Ned heard Jimmie laughing softly as he rolled on the floor.

“I’m thinkin’ what the movin’ picture men are missin’,” the boy said, as he moved forward on his hands and knees.

“This would look rather amusing – on a white canvas on the Bowery,” Ned said.

After reaching a wall, the stones of which felt damp and oozy to the touch, Ned ventured to light a match. The underground room was long and narrow, with rock walls in which there was no opening except the one by way of which the boys had entered.

Ned, by the flaring light of the match, brushed away the mould which flourished in that unwholesome place and seated himself on the stone floor, his back against the wall. Jimmie, seeking physical companionship, nestled close to him.

“Gee,” the little fellow remarked, with a snicker, “you thinkin’ of takin’ up a homestead here?”

“I’m going to remain in this room until the workers in the other chamber go away,” was the reply. “I’ve taken a notion to look into that apartment.”

“And if they don’t go away?”

“I’ll wait until they do. It is probable that they do all their work at night.”

“Then you won’t have to wait long,” the boy replied. “It was growing light in the east when we came down here.”

Jimmie dropped off into a restless sleep after a time, and Ned sat there waiting and listening, just as Frank, a short time later, waited and listened on the porch of the cottage in the jungle. When the boy awoke it was with a start of anxiety.

“The boys will think we’re dead,” he exclaimed.

“I hope they won’t try to follow us,” Ned whispered.

“If they do,” the other said, “they’ll find signs in twigs and stones all the way along. The stone heaps point the way to this place, and give the warning at the place where the stairs begin.”

Reference was here made to Boy Scout methods used in the forest. For instance, a stone with a smaller one on top says:

“This is the trail.”

Place a stone to the right of this and the meaning is:

“Turn to the right.”

One to the left means:

“Turn to the left.”

A smaller stone on top of the other two, with none at the side, means: “Be careful.”

“I hope they will keep away,” Ned went on. “It is a miracle, almost, that we got in here without being discovered.”

“What you think you’ll find in there?” asked Jimmie.

“Something concerning the plot,” was the reply.

It seemed a long time before the work in the chamber ceased, and Ned had plenty of time in which to review the strange case he was interested in. The transition from gay New York to that weird apartment seemed almost like a whiff of fancy. Then he recalled the painstaking surveillance of the fellow called “His Nobbs” on the way down, and smiled at the thought that the plans he had made at first sight of the spy had worked out remarkably well.

He had submitted gracefully to the surveillance, knowing that in time the man who was following him would track him to his camp on the Isthmus. That was the very point. He would not know where to look for the plotters, but they would know where to look for him. He depended on them to send a man to work him mischief, and reckoned on being able to follow that man back to his principals.

This they had done. The men who had employed the spy on the ship had acted quickly and had sent a bomb-thrower. Ned shuddered as he thought of the risk he had taken that night in going to bed without leaving a guard. He had overlooked a point in the game there, for he had not apprehended such prompt action on the part of the men he had pitted himself against.

However, the plan had miscarried because of his waking at the critical moment, and here he was, at the door of the men who had sent the man about their murderous work. But were these the principals? When he thought of the two who had hastened off toward Gatun in a motor car he did not believe that they were.

“I shall have to look in other places besides subterranean chambers for the men in charge,” he thought. “These fellows are merely tools.”

Presently the sharp click-click of metal came no more through the heavy air of the room, and Ned, awaking Jimmie, who had fallen asleep again, moved into the small room from which the doorway gave a view of the stairs. He could see from this room that the sun was shining brightly outside.

Ned had scarcely stationed himself in the heavy shadows back of the doorway when four men came down the passage and passed him. He had no doubt that they were the workmen going out for the day. Such work as they did must needs be done in the night.

Two of the men were tall and slim, with Spanish-looking faces, and two were short and stout, with a heavy droop to their shoulders and broad faces almost entirely covered with whiskers.

“The original anarchists,” whispered Jimmie, as the two short men passed.

After the disappearance of the workmen all was still in the underground rooms. The door to the work-chamber had been left open, and Ned knew that one of two things was the solution to this.

Either there were other men in the room, or there were watchers on the outside. He ventured out in the passage at the foot of the stairs and looked up. A roughly-dressed man stood half in view, his back to the watcher. When Ned turned back he saw Jimmie disappearing into the work-room. He called softly to him, but the boy passed on through the doorway and was lost to sight.

Annoyed at the unnecessary risk taken by the boy, Ned stepped back into the room he had just left and waited half expecting to hear a call for assistance. He knew that he could be of more assistance there than in the open doorway to the room which the boy had entered. There he would at least have the first shot if Jimmie was pursued and made for the stairs.

While he waited almost holding his breath, he grasped the bomb he had brought with him from the cottage. If Jimmie should be killed in there, the bomb should avenge his death. The ruins of the temple and the work-shop of the plotters should all ascend heavenward in one grand explosion. After a time, however, his fears were set at rest by the appearance of the boy, who came up to the doorway with a grin on his face.

“Nothin’ stirrin’ in there now,” he said. “Come on.”

It seemed plain now that those interested in the work which was going on underground were depending on outside watchers to protect them. The fire in a rude forge which stood at the distant end of the chamber was dying out when the boys reached it, and the place was only dimly lighted.

On one side of the room was a pile of gas-pipe, cut in six-inch lengths. In a corner, far away from the fire, and half buried in the earth – a great paving stone having been removed to make way for the excavation – were tin vessels tightly covered. After his experiences of the night, Ned did not have to inspect the contents of these tins. He knew very well that they contained high explosives.

“There’s stuff enough here to blow up the continent of South America,” Jimmie said, pointing at the gas-pipe lengths and the tin vessels.

“And they are getting the material in shape to do the work,” Ned added.

“Yep,” Jimmie answered. “We’ve caught ’em with their workin’ clothes on. We’ve got to the bottom of the plot.”

“You go too fast, son,” Ned replied. “We haven’t got a single clue to the men higher up. It is probable that we have discovered the plant of the men who are planning to destroy Uncle Sam’s big job, but the work we have undertaken has only begun.”

“Why, catch these men,” said Jimmie, “an’ you’ve got ’em.”

“Got these men, yes, but the chances are that even they do not know the men who are at the head of the conspiracy.”

“Some one is puttin’ money into it, anyway,” the boy suggested.

“Yes, and we don’t even know the interests which are doing it,” said Ned.

Ned now busied himself about the chamber, having closed the door so that the light of his matches would not show. There was, of course, danger that the watcher might descend the stairs and discover the closed door, but there was also the chance that he might attribute the changed situation to accident.

Presently Ned came upon a battered old writing desk standing on the head of a large barrel. The slanting top was locked down, but the boy soon had it open. Its contents consisted of two rolls of drawing paper.

Ned took them out, stirred the fire to a sudden glow, and bent over the figures and lines on the sheets. His face grew thoughtful as he looked.

“What is it?” Jimmie asked.

Ned held out the rolls.

“This one,” he said, “is a drawing of the Gatun dam, and this other is a crude sketch of the basement of the Daily Planet building in New York.”

“Gee!” cried the boy. “Are they goin’ to blow that up, too?”

“They appear to be thinking of it,” was the reply. “And there on the margin of the sheets, of each of the sheets, is a date line – Saturday, April 15th. This is the 13th.”

“Is that the date set for the explosion?” asked the boy, with wide-open eyes.

“I don’t know,” was the reply, “but it seems to me that we ought to get out of here and communicate with Lieutenant Gordon, and also with Mr. Shaw, in New York. The date marked here may be the one set for action.”

They started at once for the door, Ned taking the sheets with him and hoping to pass the guard without being seen. As they moved forward, however, they heard voices, and then a square of light told them that the door which they had left closed had been opened, and that three men were entering.

“If they turn on the light now,” Jimmie whispered in Ned’s ear, “there’ll be somethin’ doin’ here.”

The newcomers did not light the flaring torches with which the room was usually illuminated, but, closing the door, sat down near the forge.

“I think,” Ned whispered, drawing Jimmie toward the door, “that the fate of the Gatun dam and the Daily Planet building depends on our getting out of here. Move carefully.”