“There’s a light ahead, Harry!”

Frank uttered the words in an excited whisper, after they had been groping their way through the darkness of the great cavern for what seemed to be many hours.

Rattleton was greatly agitated.

“It is a light, sure!” he panted. “Frank, we’re all right at last!”

For some time they had heard a strange puffing sound that seemed smothered and far away, like the panting breathing of some subterranean monster. This was accompanied by a singular buzzing roar that sounded very uncanny.

“What is it?” asked Rattleton, in awe—“what can it be?”

“Give it up,” confessed Frank. “Let’s find out. Come on.”

They moved toward the light, and soon they found themselves looking down into a round chamber of the great cavern from a height of many feet.

What they saw filled them with inexpressible astonishment.

The place was lighted with electric lamps, and down there in the chamber was a steam engine and a small electric dynamo.

The engine was running steadily, and the dynamo hummed with a sound about which there now was nothing uncanny.

Near the engine, watching it with interest, was the girl of the golden hair.

Harry clutched Frank’s arm.

“There she is!” he panted. “We have found her at last!”

They stood in silence for several moments, watching the girl, who looked very pretty beneath the light of the electric lamps.

Suddenly a cry came from Harry, and he clutched Merriwell’s arm with quivering fingers, pointing with his other hand.

“Look! look!” he exclaimed. “The dwarf—there he is!”

Sure enough, the crouching figure of Apollo was seen emerging from the darkness of a black opening and advancing toward the girl with swift, catlike steps.

The girl had heard Harry’s exclamation, and, startled, she looked up toward where the boys were standing.

Then the dwarf rushed upon her and clutched her with his iron hands.

A scream of terror came from the lips of the frightened girl, and rang in weird echoes through the cave.

The hand of Apollo was pressed over her mouth.

But that scream had been heard, and there was an answering shout from not very far away.

The girl struggled, but the dwarf dragged her along toward the dark opening.

“How can we get down there, Frank? We must take a hand! How can we do it? It is too far to jump!”

Rattleton was frantic.

Frank was looking for some way of getting down into the chamber.

Before either of them could discover a means of going to the assistance of the girl, Carter Morris, the strange old hermit, rushed into the cavern.

Morris sprang to the aid of the girl, but it seemed Bernard Belmont had been waiting for such a thing to happen, for he leaped out of the darkness and grappled with the hermit.

Then a savage battle took place before the eyes of the boys.

“Furies!” roared the man of the cave, writhing to break the grasp of his assailant. “Who are you?”

The girl got her mouth free from Apollo’s hand and screamed:

“It is my stepfather—it is Bernard Belmont!”

It seemed that those words filled the hermit with a mad frenzy. He struggled furiously, and Belmont was forced to exert all his strength to prevent himself from being overcome, although he was the assailant.

“We must go to the rescue, Frank—we must!” palpitated Rattleton.

The boys were determined to find a way of getting down into the round chamber, and Frank fancied he saw a manner of descending. It would be necessary to drop at least fifteen feet, but he started to make the attempt and Harry followed.

The battle between Belmont and Carter Morris continued with great fury, and Morris seemed to become perfectly mad with rage when he was unable to overcome his assailant.

Bit by bit the hermit dragged the man toward the buzzing dynamo, his eyes glowing with an awful purpose.

Suddenly he tried to hurl Belmont upon the dynamo.

Belmont realized the intention of the man, and a scream of fear escaped him.

A moment later both men went down upon the machine!

A second they seemed to cling there, and then they were flung off, falling upon the rocky floor of the cavern and lying still, holding fast to each other in death!

The girl screamed, and the dwarf seemed overcome with sudden fear. He stared at the contorted face of his dead master, seeming unable to realize what had happened in the twinkling of an eye.

Down from the heights above dropped two boys.

“Give it to him, Frank!” screamed Harry.

They rushed at the dwarf, but, for once in his life, at least, Apollo was mastered by terror, for, with a shout of dismay, he released the girl and fled, disappearing in a hopping, bounding manner into the darkness.

Rattleton caught the half-fainting girl in his arms, crying:

“Hurrah, Merry, we have found her, and we’ve saved her!”

But she had fainted.

When another morning dawned the two boys and the girl left the great cave and started for Carson City.

Already had Mildred explained to them how it happened that the steam engine and the dynamo were found in the cavern. The coiners who had occupied that retreat years before had discovered a valuable vein of ore, and they had devised a scheme of mining with the aid of electricity. The engine was brought there to run the dynamo. As a certain portion of the cave yielded coal in liberal quantities, it was not difficult to find fuel for the engine.

Carter Morris, being somewhat of an electrician, had put the abandoned machinery in running order when he took possession of the cave.

It had been his intention to protect himself from intruders by the aid of electric currents, and he had given Frank and Harry a frightful shock at the mouth of the cavern by means of hidden wires.

The electric current had caused his death when he fell upon the dynamo in struggling with Bernard Belmont.

The graves of both men were made in the cave, and Little Milly shed tears over the body of her mad uncle, who had sought to befriend her by “burying” her.

The hidden bicycles were found, and the sailboat was discovered where the boys had left it.

After setting sail to cross the lake, Frank touched Harry’s arm and pointed to an object that was floating in the water, at the same time pressing a finger to his lips and shaking his head, with a look toward Milly.

Harry looked and started, for he saw the ghastly, upturned face of Apollo, the dwarf, the scar on his cheek having turned a purplish blue.

The girl did not see this object, and the boys believed it far better to leave the dwarf than to horrify her by letting her see the body.

Carson was reached without further adventure, and there a joyous surprise awaited Mildred Morris.

Jack Diamond met the little party outside the hotel.

“Where are Toots and Bruce?” asked Frank, in a low voice.

“Standing guard, as you directed,” said Jack. “We have taken turns since you went away, and he has not been left alone a moment.”

“How is he?”

“Better—much better. The doctor says he thinks he’ll come around all right.”

Then Frank and Harry accompanied Milly to a certain room of the hotel. Browning and the colored boy were called out of the room, and Merriwell said to the girl:

“Go in, Miss Morris. There’s some one in there who will be glad to see you.”

He held the door open, and urged her gently into the room.

A moment later there was a cry of joy—two cries—a rush. Then, peering in at the door for a moment, the delighted lads saw Milly spring toward the bed and clasp her living brother in her arms.

Frank closed the door.

Immediately Toots danced a wild cancan of delight.

“Golly sakes teh goodness!” he chuckled. “Dat gal sho’ am a peach. I’d jes’ lek teh take dat sick boy’s place ’bout five minutes. Yah! yah! yah! Oh, mommer!”

The boy whom Mildred had rushed to meet was her brother, George, who was not dead, but had fainted at sight of his cruel stepfather and the dwarf. Belmont had thought the boy dead, and had left Carson without delay, much to the satisfaction of Frank Merriwell.

And now the doctor who was attending George said the boy had a fair show to recover.

“Say,” observed Diamond, suddenly, “the buried heiress is out of sight! I think I will——”

“If you try it,” spluttered Rattleton, menacingly, “I’ll hake your bread—I mean I’ll break your head! I saw her first, and I have first claim there!”

“Break away, there, you chumps,” laughed Frank. “We have business first, you know. We must speed on toward California and bring this wonderful trip of ours to a successful finish. Onward is the cry.”

That afternoon they bade farewell to George and Mildred, and rode away, sorry indeed at the parting.