CHAPTER XXII.

THE HIDDEN DOOR.

the boys looked frantically for a hiding place. There was none. They pressed themselves against the boxes. The footsteps became louder.

Then the man walked past. After he trudged by, the Hardys sighed in relief.

"Another close call like that, and I'll be a nervous wreck," murmured Joe.

"Did you notice what he was carrying?"

"I thought it was a machine gun."

Frank shook his head. "That's what I thought at first. But it wasn't. I got a good look at it when he went by. It was a power drill."

"Like the one we found in the scarecrow?"

"Exactly like it. Maybe the same one. I think-----"

"Sh-h! Listen!"

Off down the pa.s.sageway they heard more footsteps. The fellow with the power drill had gone up the stairs into the upper part of the shaft. But now someone else was approaching.

They heard the voices of two men, echoing in the rocky pa.s.sage.

Hardly daring to breathe, the boys crouched in their hiding place and waited. The men drew closer, then stopped at the entrance to the tunnel. They were pushing a cart, which seemed to be heavy.

The brothers wondered if the men had caught a glimpse of them. But apparently they merely halted to rest a moment. In the cart were several large pieces of pale blue rock.

"Nice stuff," one of the workmen said.

"I wonder if the old timers who dug iron ore out of this mine knew about it," remarked the other.

'' Back in Eevolutionary days they never even dreamed of cobalastium. It's a lot more valuable than iron."

"Especially now. The government is trying to round up a lot of it. Well-let's go.''

They put the ore back in the cart and went on. Presently they disappeared.

"This mine is being worked, but not for iron," said Joe quietly. "Whatever those fellows are doing with it, they keep it a secret. Let's go on a little farther and find out what we can."

A few moments later they could see miners at work, drilling in the rock wall. The boys dared go no closer. Curious, they decided to investigate a narrow tunnel, branching off the main pa.s.sageway. It was dark. Frank took a flashlight from his pocket and switched it on.

183 The beam revealed grim, rough-hewn walls vanishing into blackness.

"Look!" whispered Joe. "A pile of torch handles!"

These were stacked on a small ledge at one side of the corridor. There were several dozen of them.

"Maybe we'd better take along a couple. They may come in handy," advised Frank.

The brothers each took one, then hurried through the tunnel. It continued on and on, winding underground. The floor was deep in dust and soot. In it were human footprints. The boys crouched and examined them.

"Looks as if this channel is used, even if it isn't lighted," Frank remarked.

'' But only by one person!'' Joe had his own flashlight out now and was scrutinizing the footprints closely. "Don't you see-they're all alike. All the same size, coming and going. And they are all certainly made by the same pair of shoes."

Mystified, the boys followed the tunnel farther. Here and there in the walls they found places where holes had been bored. For a time these puzzled them, until at last they came to a torch handle, projecting from the rocks.

"I'm beginning to see through this torch business," Frank said. "In the olden days, when this mine was originally worked, the pa.s.sages were lighted by torches. Probably they 184 held pine pitch. That explains the pile of han dies we've found."

"I'm beginning to have a few ideas about the/ ones in Asa Grable's laboratory,"

remarked Joe. "Do you know what I think? This tunnel leads under the Grable property.''

'' You may be right. It runs in that direction. And the Wortman cottage isn't far from Grable's place."

Frank hurried on. Joe's suggestion filled him with excitement. The existence of the pa.s.sage might be the solution to a great many things. It might explain, for instance, how thieves got into the Grable greenhouses without setting off the burglar alarm. He mentioned this to Joe.

"But what would the flickering torch gang want with silkworms?" Joe objected.

"If I could answer that, the whole mystery Would be solved. But I think we're going to find out," declared Frank.

They stumbled on down the dusty old tunnel. At last it came to an end-but not to another pa.s.sage; not in any subterranean chamber; not in any shaft leading to the outside world. It simply came to an end, sloping sharply and narrowing down until it was only a few feet wide.

'' That's strange,'' Frank muttered. '' Footprints in the dust, so somebody has used this pa.s.sage. But it doesn't lead anywhere."

185 He turned his flashlight full on the end of the tunnel. A pile of rocks, one on top of the other, blocked any further progress. Frank stepped forward and pulled at the rocks with all his strength.

To his astonishment they moved. There was a dismal creaking of hinges. The rocks suddenly moved toward him, then swung to one side. A door opened as if by magic.

Joe whistled. "Pretty neatl" he exclaimed.

The wooden door had a projecting base on each side. On these, rocks were piled up.

Thus it could be closed from either side without disturbing the rocks, which apparently were there to hide the door from view.

Cautiously, the Hardy boys pa.s.sed through the strange entrance. The flashlights showed them a heavy wooden barrier a few feet away. Frank grasped the k.n.o.b, tried to open it.

It was locked.

What mystery lay behind that locked door? Perhaps it guarded the secret to all the strange events that had puzzled them.

Suddenly, just beyond it, they heard footsteps descending a flight of stairs. Slow footsteps, thudding solemnly-approaching the door! Then came the rattle of a chain.

'' Quick!'' gasped Frank. '' Get back into the tunnel!"

The boys scrambled swiftly through the rock doorway, and swung it shut after them. But 186 they did not close it entirely. They heard the other wooden door creak open slowly. The Hardys, peeping through the narrow slit they had left, saw Asa Grable standing on the threshold!

CHAPTER XXIII.

THE SMELL OF DANGER.

ready to slam the door shut and hold it against capture, the Hardy boys watched Asa Grable.

The elderly scientist was revealed plainly in the glare of an electric light hanging from the ceiling at the foot of the stairs. He was muttering to himself. Under one arm he carried a large square gla.s.s jar full of earth.

Instead of proceeding farther, he set the jar carefully on the floor and turned back.

Evidently this was a closet he used for special experiments. He did not close the door behind him. The boys saw him putter around for a moment in the room beyond. Then he ascended the stairs. His echoing footsteps became fainter and fainter, then died away.

The brothers glanced at each other. Should they follow Asa Grable? Perhaps he had merely gone back for something he had forgotten. Frank decided that they should watch the man's movements. There was too much at stake not to do so. In a moment the boys had closed the rock doorway and were across the threshold of the other one. Silently they pro*

ceeded up the steep flight of stairs.

Light fell through a half-open doorway at the top of the steps. There, crouching in the shadows, Frank and Joe peered into the room beyond.

It was Asa Grable's secret laboratory, where Joe had witnessed the synthetic rubber experiment. In the glow of light from a solitary desk lamp they saw the elderly scientist examining a solution in a test tube. Then, quite unaware of the eager eyes watching him, he turned away from the table and went over to a cupboard. He unlocked the door. When he turned around, he was carrying over one arm a long black robe.

The Hardy boys were stunned!

They could scarcely believe what they saw. Joe's discovery of the torch handles in Grable's laboratory had been damaging enough. Their coming upon the secret tunnel that led directly to the scientist's laboratory had been equally suspicious. But they were not prepared for this final clue, with all its implications that Asa Grable was actually one of the hooded men.

"Mr. Grable!" called a familiar voice.

The scientist looked up. '' I 'm coming, Archibald, '' he answered. '' I 'm coming right away.''

Down the stairs from the office came Archibald Jenkins. He was carrying a torch handle. The younger man seemed fl.u.s.tered and anxious.

"I called to you a few minutes ago but you didn't answer," he said, handing Asa Grable the torch handle.

189 "Guess I didn't hear you, Archibald," returned the scientist mildly. "I'll come along right away."

Archibald Jenkins returned up the stairs again. The elderly scientist followed. The Hardy boys could hear the murmur of their voices, but they could not distinguish what the two men were saying. A door swung shut at the head of the stairs.

Frank and Joe darted into the secret laboratory. Lightly they sped up the steps, until they reached the closed door at the head of the flight. They were just in time to hear Archibald Jenkins say: "All right then, I'11 tell them two o'clock. Is that satisfactory?"

"Two o'clock sharp," answered Asa Grable.

"Fine. In the meantime, you'd better get some sleep. It will be a hard ordeal for you."

"Yes, I suppose I should go to bed and get a little rest," the scientist agreed. "Turn out the light, Archibald. Be sure to lock all the doors before you leave."

"Don't worry. I'll see that everything is locked up tight. Good night."

"Good night, Archibald."

The Hardys heard a door open and close. They could see a crack of light beneath the door of the office. Archibald Jenkins was moving about alone. Finally the light was extinguished and the man's footsteps receded. The 190 The Flickering T rch Mystery boys were by no means certain that Jenkins had left the building. He might have gone into another office.

"I think we've learned all -we're going to learn here,'' whispered Frank. '' And we might be caught getting out of here, if the burglar alarm should go off. Let's go back into the mine."

"Suits me." Joe turned and made his way quietly down the stairs. "I wouldn't want to run into Archibald Jenkins at this stage of the game. He might think we know too much."

The boys returned to the secret laboratory but they did not linger there. They went oil down the second flight of stairs, through the doorway into the tiny pa.s.sage, and through the rock doorway. Frank glanced at his watch.

"Ten o'clock," he said quietly. "We still have time to do some more exploring here, if nothing big is going to happen until two o'clock."

"You could have sold me out for a nickel when I saw Grable take that black robe out of the closet," Joe declared. "To think of him him being one of the hooded men!" being one of the hooded men!"

"Of course we could be wrong."

"That robe settles it so far as I'm concerned. And what's going on at two o'clock? Do you think there's to be a meeting of the flickering torch outfit?"

"It might be." Frank was puzzled. "This 191 ought to clear up the mystery for us, but it doesn't. It only makes everything more puzzling than ever. Is Qrable robbing his own, greenhouses ?''

"That's what I keep asking myself. Maybe Ms greenhouses haven't been robbed at all.

Perhaps that's just a blind, so that if we notice anything suspicious going on around here, it can be blamed on burglars.''

There seemed to be no satisfactory explanation. From the beginning the Hardy boys had trusted Asa Grable, had seen no reason to doubt his word about the robberies. And yet the black robe and the torches were so incriminating that they seemed to offer only one answer.

In silence the boys made their way back down the long, narrow tunnel. Suddenly Joe sniffed.

"Notice that odor?"

They could detect a faint, pungent scent in the tunnel. As they proceeded, it became stronger.

"Must be a skunk loose in the mine," chuckled Joe. "Whew! That's mighty powerful. I hope we don't run into him."

He advanced a few more paces. But Frank came to a sudden stop.

"Joe! Come back!" he said sharply.

His brother turned. "What's the matter! You aren't afraid of a nice little black and white skunk, are you?"

Frank grabbed Joe's arm, hurriedly pulled 192 him back along the tunnel. "That odor means danger," he snapped urgently. "We must get out of here. And quickly!''

He hustled Joe back along the tunnel. Then he broke into a run. His brother was completely mystified.