"Father's gone!" she cried, despairingly.

Locke threw himself full against the door at the head of the cellar stairs which the men had slammed shut. He tried to batter it down, but it was too strongly built. Then he drew his revolver and with the barrel started to push out the pins from the hinges. He worked feverishly and succeeded in driving the top pin out. Then, using it as a lever, he was able to pull the door from its frame.

He dashed down the stairs, but was late by only the fraction of a second, as a metal hand was just closing the huge door to the Graveyard of Genius. He fumbled at the secret combination, and as he was doing so Eva and Zita joined him.

The door swung open and they rushed through. But the place was deserted.

"They've carried your father through some secret passage," exclaimed Locke. "That would explain much that is strange that has happened about the house, too."

Just then Zita stepped forward with the plan in her hand. "See," she cried, "there is a secret passage marked on this."

Locke studied the plan for some time, but whoever had drawn it had carefully concealed both the exact location of the passage and the method by which it was reached. As he searched, however, an idea occurred to Locke.

"I'll rig a trap with a camera," he decided, finally.

A few minutes later he returned to the room with his special quick-shutter camera, a flash-bag, and a ball of light twine. Carefully he focused the camera on the wall where the plan showed the secret passage to be. Then he rigged up the flash-bag and connected the whole with the twine, which he strung all about the Graveyard of Genius, so that, should any part of the wall move, it would cause the twine to break which in turn would at the same time release the shutter of the camera and explode the powder of the flashlight. Thus, without any direct human agency, a photograph would be taken.

Next he attached wires and ran them to the library above, where he installed an annunciator, the needle of which would indicate when the trap was sprung and the picture taken. Fascinated, the two girls watched. Eva was almost fainting with grief at the terrible fate that had overtaken her father. Even in his sickness, at least she had had him. But now he was gone--to what she could only guess. Locke tried to console her as they paced the library above, even though he realized that such consolation was hollow.

It was perhaps half an hour later when suddenly the needle of the annunciator began to vibrate rapidly. All leaped to their feet and ran down the stairs to the Graveyard.

At once Locke rushed to the camera, put in a slide, and took out the plate-holder. Then they hurried up to his laboratory.

There Locke procured a developing-bag and started to work. Nervously and impatiently Eva and Zita watched him at his task.

At last the negative was ready and Locke drew it from the bag and held it to the light.

There, glaring out of the plate, was the devilish face of Balcom!

Eva and Zita both uttered a cry of astonishment and consternation. Even Locke was amazed. But the strongest feeling he had was anger as he turned to them.

"You two take this plan," he exclaimed. "It shows a den with an exit indicated. Get some one to go with you; find the place and wait for me there. I can find the secret entrance from the Graveyard from this negative--and I'm going through it."

Balcom, in the passageway between the Graveyard of Genius and the Automaton's den, was livid with fury. He realized that his picture had been taken, surmised that the secret passage would be found and that some assault on the den would be attempted. But he had had no time to locate the camera, which Locke had hidden well, nor had he dared to search longer for it when he heard Locke bounding down the stairs from the library.

Accordingly, he had retreated and hastened back through the passageway into the Automaton's den.

"Quick!" he shouted to the horde of emissaries in the place. "Bring dynamite, electric wires, and a rack-bar. They think they have us trapped. But if they try to follow me here, I tell you it will mean certain death to them."

The emissaires hastened to obey him. They brought the explosive and the means to detonate it, and carried the stuff into the passageway, where they made the connections. An emissary stepped forward and volunteered to use the rack-bar when the time came, but Balcom waved him away.

"No," he growled. "No one can take my revenge from me. I'll do the killing."

The emissaries fell back and went into the den.

Balcom was making some final adjustments when the great rock separating the passageway from the Graveyard of Genius swung slowly on its balanced hinges.

Startled from his work, even though he had expected the thing, Balcom looked up, and in the passageway caught a glimpse of the dim outline of his arch-enemy, Locke.

Balcom had been right. Locke had found the clue to the secret entrance to the tunnel.

He worked feverishly to complete the final connection, but almost before he finished Locke charged and the battle was on.

Up and down the passageway they fought. Although Locke was the younger man, yet in Balcom he found a giant of strength.

It was a fight between these two alone, for no emissary, no Automaton, now entered that passage of death.

Neither uttered a sound. Neither had a weapon. It was the primitive struggle of man to man for life.

But now Locke's youth and clean living began to tell in his favor and he sensed that his adversary was weakening. He redoubled his efforts.

After a particularly vicious blow from Locke, Balcom threw up his hands and toppled over backward--in the direction of the rack-bar itself.

Locke tried to throw Balcom's body out of the way. It was too late. With a thud Balcom crashed full upon the plunger, driving it home.

There was a blinding flash, a dull roar, and the earth rocked. Huge boulders were tossed about like feathers and the roof of the passage caved in.

Balcom was killed instantly. Locke, with better fortune, had been hurled to the ground, where the earth and rocks, in falling, had formed a sort of arch over his body.

He was alive, though barely conscious. He knew that soon a search would be made for him. But, buried under tons of earth and rock, could any rescuers reach him in time? Was this the end?

CHAPTER XXIV

For a long time Locke lay quite still. The shock to his nervous system had been terrific, and, although physically almost uninjured, he had lost his usual grip on himself and felt very helpless.

He felt terribly tired. The thought came to him that he had done enough, reached his limit of endurance. He craved sleep, a long sleep, and forgetfulness.

But youth and the undying desire for life and accomplishment won over this deadly mood and he began to take note of his position. His mind became clearer and the ringing in his ears, caused by the explosion, gradually passed away.

Then, like a flash, the question entered his mind of how he was able, buried under tons of debris, to breathe so freely. Why was the air not vitiated?

He tried to move slowly and quietly so as not to dislodge any of the rocks that formed an arch over his body. He succeeded beyond his expectations, for his body was in a sort of natural pocket and not one of his limbs was inextricably bound. Thus, twisting his body, he managed to draw himself into what seemed to be an even more open space.

He hardly dared to breathe, so fearful was he that any moment he might reach a point where further progress would be impossible. He moved slowly, gropingly, then suddenly he recoiled in horror, for his hand had come in contact with something which he recognized to be a man's face.

In his shaken condition it was some seconds before he could control the wild jangling of his nerves. Then he searched his pockets and, finding a match, lighted it. There, covered to the armpits by dirt and rocks, was the body of Balcom, whose last act before his own death had been an attempt to murder Locke.

Locke shuddered and redoubled his efforts to escape from the gruesome place. There still remained a small hole through which he must climb.

But he negotiated it successfully, and in another moment he was aboveground and free.

Eva and Zita had followed Locke's instructions, but had not waited to find any one to go with them to the exit from the den. Nor did they wait at the exit more than a few minutes.

Eva had taken a small electric torch with her, and, becoming impatient at the non-appearance of Locke, she flashed it about as she followed the lines and marks indicated on the plan of the den.

She and Zita were surprised at the magnitude of the entrance passageway they uncovered. They had had to make a detour in order to reach the beach at a point where it was indicated that the exit of the den would be found, and even with the plan, which they consulted at every step, they almost missed their objective, for the cleft in the rocks slanted inward and was difficult to see even when one was standing directly in front of it.