Surprise held Tom and his friends almost spellbound for the moment. The young inventor's hand went toward the pocket where he carried his revolver. Mr. Jenks, who had the only other weapon, sought to draw it, but he was stopped by a gesture of one of the two men with guns.

"Hold on, strangers!" the man cried. "I know what you're up to! Better not try to draw anything--it might not be healthy. Now, then, who are you, and what do you want?"

The question came rather as a surprise, at least to Tom and Mr. Jenks. They had taken it for granted that these men--if they were the diamond makers--would know Mr. Jenks, and guess at his errand in coming back to Phantom Mountain. But, it seemed, that they took them all for casual strangers.

No one answered for a moment. Tom caught the eye of Mr. Jenks, and there was a look of hope in it. If ever there was a time for strategy, it was now. Evidently Munson, the stowaway on the airship, had not yet been able to send a warning to his confederates. And neither of the two men recognized Mr. Jenks as the man who had been defrauded of his rights. It might be possible to conceal the real object of the adventurers until they had time to formulate a plan of action.

"Well," exclaimed the man with the gun, impatiently, "I ask you folks a question. What do you want?"

Fortunately, neither Mr. Damon nor Mr. Parker replied. The former because he deferred to Tom and Mr. Jenks, and the scientist because he was busy inspecting some curious rocks he picked up. As it turned out this was the luckiest thing he could have done. It lent color to what Mr. Jenks said a moment later.

"What are you doing up here?" demanded the man again. "Don't you know this is private property?"

"We--we were just looking around," answered Mr. Jenks, which was true enough; as far as it went.

"Prospecting," added Tom.

"After gold?" demanded the second man, suspiciously.

"We'd be glad to find some," retorted the lad. At that moment Mr. Parker began breaking off bits of rock with a small geologist's hammer which he carried. The men with the guns looked at him.

"So you think you'll find gold up here?" asked the one who had first spoken.

"Is there any?" inquired Tom, trying to make his voice sound eager.

"Nary a bit, strangers," was the answer, and the two men laughed heartily. "Now, we don't want to seem harsh," went on the man who seemed to be the spokesman, "but you'd better get away from here. This is private ground, and dangerous too--how'd you ever get up the trail--we heard it was destroyed."

"There is still a narrow path," said Mr. Jenks. "We came up that--the lightning and landslide haven't left much of it, though."

Mr. Parker looked quickly up from the rocks at which he was tapping with his small hammer. "You have terrific lightning up here," he said. "I am much interested in it, from a scientific standpoint. I predict that some day the entire mountain will be destroyed by a blast from the sky."

"I hope it won't be right away," spoke one of the men. "Now I guess you folks had better be leaving while there's a path left to go down by."

"Might I ask," broke in Mr. Parker, as calmly as though he was lecturing to a class of students, "might I ask if you have noticed any peculiar effect of the lightning up here on the summit of the mountain? Does it fuse and melt rocks, so to speak?"

"What's that?" cried the spokesman, with a sudden flash of anger. The two men looked at each other.

"I wanted to know, merely for scientific reasons, whether the lightning up here ever melted rocks?" repeated Mr. Jenks.

"Well, whether it's for scientific reasons or for any other, I'm not going to answer you!" snapped the man. "It's none of your affair what the lightning does up here. Now you'd all better 'vamoose'--clear out!"

"All right--we'll go," said Tom, quickly, at the same time motioning to Mr. Jenks to agree with him. The eyes of the young inventor were roving about. He saw what looked like a second trail, leading down the mountain, from the far side of the cave. He was convinced now that there was another way to get to it. Possibly they might find it. At any rate nothing more could be done now. They must go back, for the cavern was too well guarded to attempt to enter it by force--at least just yet.

"Yes, we'll go back," assented Mr. Jenks.

Mr. Parker was tapping away at the rocks. He looked toward the black mouth of the big cave. On what corresponded to the roof of it, some distance back from the entrance, he saw a slender metal rod sticking up into the air.

"May I ask if that's a lightning rod?" he inquired innocently. "If it is, I should like to ask about its action in a mountain that is so impregnated with iron ore.

"You may ask until you get tired!" cried the spokesman, again showing unreasoning anger, "but you'll get no answer from us. Now get away from here before we do something desperate. You're on private ground and you're not wanted. Clear out while you have the chance."

There was no help for it. Slowly our friends turned and began to go down the dangerous trail. They were soon out of sight of the two men who stood before the cave, with their guns ready, but neither Tom nor any of his companions spoke for some time.

When they had rounded one of the most dangerous turns the young inventor sat down to rest, an example followed by the others.

"Well," asked Tom, "do you think those are some of the diamond makers, Mr. Jenks?"

"I certainly do, though I never saw those two men before. If I could once get inside the cave, I could tell whether or not it was the one where I was practically held a prisoner. But I'm sure it is. I know some of the men used to go off every day with guns, and not come back until night. I have no doubt they were on guard, just as these two are. And, also, I think I heard them speak of a second entrance to the cavern. The one we just saw may not be the main one, through which I was taken."

"I believe we are on the right track," ventured Mr. Damon, "but we will either have to go up there after dark, which will be risky, on account of the narrow trail, or else we will have to find some other path."

"The last would be better," spoke Tom.

"That rod of metal sticking up on top of the cave interested me," said the scientist. "Did you hear anything of that when you were here before, Mr. Jenks?"

"No. Probably that is only a lightning rod, or it may be a staff for a signal flag. But what surprises me is that those men didn't suspect that we were seeking to discover their secret. They took us for ordinary prospectors."

"So much the better," remarked Tom. "We have a chance now of getting inside that cave. But we will have to go back to camp, and make other plans. And we must hurry, or it will be dark before we get there."

They hastened their steps, pausing only briefly to eat some of the lunch they had brought along, and to drink from a spring that bubbled from the side of the mountain. It was getting dusk when they got back to their tent. They found nothing disturbed.

"I wonder if we'll see that phantom again to-night?" ventured Tom, as they were sitting about the campfire a little later.

"Probably not," remarked Mr. Jenks. "I don't believe the ghost will venture down the dangerous trail after dark, and the gang may think that the warning given us by the two men on guard at the cave will be sufficient. But if we don't leave here by to-morrow I think we will have another visit from the thing in white."

It was about an hour after this when Tom was collecting some wood in a pile nearer the fire, so as to have it ready to throw on, in case there was any alarm in the night, that he happened to look up toward the summit of the mountain. A slight noise, as of loose stones rolling down, attracted his attention, and, at first, he feared lest another landslide was beginning, but a moment later he saw what caused it.

There, advancing down the steep and dangerous trail was the figure in white--the phantom. Instantly a daring plan came into Tom's head. Dropping the wood softly, he moved back out of the glare of the fire.

"Mr. Jenks!" he called in a whisper.

The diamond man, who was behind the tent, came toward Tom.

"What is it?" he asked. Then, as he saw the ghostly visitor, he added: "Oh--the phantom again! What's it up to?"

"The same thing," replied Tom, "but it won't do it long, if my plan succeeds."

"What plan is that, Tom?"

"I'm going to try to capture that--that man--or whatever it is. Will you help?"

"Surely!"

"Then let's work around behind it, while Mr. Damon and Mr. Parker come up from in front. We'll solve this part of the mystery, anyhow, if it's possible!"

The two other men were soon told of the plan. Meanwhile the thing in white had advanced slowly, until within a few hundred feet of the camp. They could see now that it was no shaft of light, but some white body, shaped like a tall, thin man, draped in a white garment. The long arms waved to and fro. There was no semblance of a head.

"You and Mr. Parker go right toward it, slowly, Mr. Damon," advised Tom. "Mr. Jenks and I will make a circle, and get in back. Then, if it's anything alive we'll have it."

The "ghost" continued to advance. Tom and the diamond man stole off to one side, their buckskin moccasins making no sound. Mr. Damon and the scientist went boldly forward.

This movement appeared to disconcert the spirit. It halted, waved the arms with greater vigor than before, and seemed to indicate to the adventurers that it was dangerous to advance. But Mr. Damon and Mr. Parker kept on. They wanted to give Tom and Mr. Jenks time enough to make the circuit.

Suddenly the stillness of the night was broken by a low whistle. It was Tom's signal that he and Mr. Jenks were ready.

"Come on! Run!" cried Mr. Damon.

The scientist and the eccentric man leaped forward.

The "ghost" heard the whistle, and heard the spoken words. The thing in white hesitated a moment, and then raised one arm. There was a flash of lire, and a loud report.

"He's firing in the air!" cried Tom. "Come on, we have him now!"

Undaunted by the display of firearms, Mr. Damon and Mr. Parker kept on. They could hear Tom and Mr. Jenks running up in back of the figure. The latter also heard this, and suddenly turned. Caught between the two forces of our friends, the "ghost" was at a loss what to do.

The next instant Tom, who had distanced Mr. Jenks, made a flying tackle for the figure in white, and caught it around the legs. Very substantial legs they were, too, Tom felt--the legs of a man.

"Wow!" yelled the "ghost," as he went down in a heap, the revolver falling from his hand.

"Come on!" cried Tom. "I have him!"

His friends rushed to his aid. There was a confused mass of dark bodies, arms and legs mingled with something tall and thin, all in white. Suddenly the moon came from behind a cloud and they could see what they had captured--for captured the phantom was.

It proved to be a rather small man, who wore upon his shoulders a framework of wood, over which some white cloth was draped. It had fallen off him when Tom made that tackle.

"Well," remarked the young inventor, as he sat on the struggling man's chest. "I guess we've got you."

"I rather guess you have, stranger," was the cool reply.