Del Mar read it with a scowl of fury. Then he seized his hat, and a short hunter's axe, and disappeared through the panel into the subterranean pa.s.sage which took him by the shortest cut through the very hill to the sh.o.r.e.

Slowly Arnold and Woodward made their way along the sh.o.r.e, carefully searching for the spot where they had seen the house with the aerial.

At last they came to a place where they could see the deserted house, far up on the side of a ravine above a river and a waterfalls. They dived into the thick underbrush for cover and went up the hill.

Some distance off from the house, they parted the bushes and gazed off across an open s.p.a.ce at the ramshackle building. As they looked they could see a man hurry across from the opposite direction and into the house.

"As I live, I think that's Del Mar," muttered Arnold.

Woodward nodded, doubtfully, though.

In the house, Del Mar hurried to a wall where he found and pressed a concealed spring. A small cabinet in the plaster opened and he took out a little telephone which he rang and through which he spoke hastily.

"Pull in the wires," he shouted. "We're discovered, I think."

Down in the wireless station in the cave, the operator at his instrument heard the signal of the telephone and quickly answered it.

"All right, sir," he returned with a look of great excitement and anxiety. "Cut the wires and I'll pull them in."

Putting back the telephone, Del Mar ran to the window and looked out between the broken slats of the closed blinds. "Confound them!" he muttered angrily.

He could see Arnold and Woodward cautiously approaching. A moment later he stepped back and pulled a silk mask over his upper face, leaving only his eyes visible. Then he seized his hunter's axe and dashed up the stairs. Through the scuttle of the roof he came, making his way over to the chimney to which the wireless antennae were fastened.

Hastily he cut the wires which ran through the roof from the aerial. As he did so he saw them disappear through the roof. Below, in the cave, down in the ravine back of the falls, the operator was hastily hauling in the wire Del Mar had cut.

Viciously next, Del Mar fell upon the wooden aerial itself, chopping it right and left with powerful blows. He broke it off and threw it over the roof.

Below, Arnold and Woodward, taking advantage of every tree and shrub for concealment, had almost reached the house when the broken aerial fell with a bang almost on them. In surprise they dropped back of a tree and looked up. But from their position they could see nothing.

Together they drew their guns and advanced more cautiously at the house.

Del Mar made his way back quickly over the roof, back through the scuttle and down the stairs again. Should he go out? He looked out of the window. Then he went to the door. An instant he paused thinking and listening, his axe raised, ready for a blow.

Arnold and Woodward, by this time, had reached the door which swung open on its rusty hinges. Woodward was about to go in when he felt a hand on his arm.

"Wait," cautioned Arnold. He took off his hat and jammed it on the end of a stick. Slowly he shoved the door open, then thrust the hat and stick just a fraction of a foot forward.

Del Mar, waiting, alert, saw the door open and a hat. He struck at it hard with the axe and merely the hat and stick fell to the floor.

"Now, come on," shouted Arnold to Woodward.

In the other hand, Del Mar held a chair. As Woodward dashed in with Arnold beside him, Del Mar shied the chair at their feet. Woodward fell over it in a heap and as he did so the delay was all that Del Mar had hoped to gain. Without a second's hesitation he dived through an open window, just as Arnold ran forward, avoiding Woodward and the chair. It was spectacular, but it worked. Arnold fired, but even that was not quick enough. He turned and with Woodward who had picked himself up in spite of his barked shins and they ran back through the door by which they had entered.

Recovering himself, Del Mar dashed for the woods just as Arnold and Woodward ran around the side of the house, still blazing away after him, as they followed, rapidly gaining.

Elaine changed her clothes quickly. Meanwhile she had ordered horses for both of us and a groom brought them around from the stables. It took me only a short time to jump into some dry things and I waited impatiently.

She was ready very soon, however, and we mounted and cantered off, again in the direction of the sh.o.r.e where she had seen the remarkable waterfall, of which she had told me.

We had not gone far when we heard sounds, as if an army were bearing down on us. "What's that?" I asked.

Elaine turned and looked. It was a squad of cavalry.

"Why, it's Lieutenant Woodward's friend, Captain Price," she exclaimed, waving to the captain at the head of the squad.

A moment later Captain Price pulled up and bowed. Quickly we told him of what Elaine had just discovered.

"That's strange," he said. "This man--" indicating the sailor--"has just told me that Lieutenant Woodward and Professor Arnold are investigating a wireless outfit over near there. Perhaps there's some connection."

"May we join you?" she asked.

"By all means," he returned. "I was about to suggest it myself."

We fell in behind with the rest and were off again.

Under the direction of the sailor we came at last to the ravine where we looked about searchingly for some trace of Arnold and Woodward.

"What's that noise?" exclaimed one of the cavalrymen.

We could hear shots, above us.

"They may need us," cried Elaine, impatiently.

It was impossible to ride up the sheer height above.

"Dismount," ordered Captain Price.

His men jumped down and we followed him. Elaine struggled up, now helped by me, now helping me.

Further down the hill from the deserted house which we could see above us at the top was an underground pa.s.sage which had been built to divert part of the water above the falls for power. Through it the water surged and over this boiling stream ran a board walk, the length of the tunnel.

Into this tunnel we could see that a masked man had made his way. As he did so, he turned for just a moment and fired a volley of shots.

Elaine screamed. There were Arnold and Woodward, his targets, coming on boldly, as yet unhit. They rushed in after him, in spite of his running fire, returning his shots and darting toward the tunnel entrance through which he still blazed back at them.

From our end of the ravine, we could see precisely what was going on.

"Come--the other end of the tunnel," shouted Price, who had evidently been over the ground and knew it.

We made our way quickly to it and it seemed as if we had our man trapped, like a rat in a hole.

In the tunnel the man was firing back at his pursuers as he ran along the board walk for our end. He looked up just in time as he approached us. There he could see Price and his cavalry waiting, cutting off retreat. We were too many for him. He turned and took a step back.

There were Arnold and Woodward with levelled guns peering in as though they could not see very clearly. In a moment their eyes would become accustomed as his to the darkness. What should he do? There was not a second to waste. He looked down at the planks beneath him and the black water slipping past on its way to the power station. It was a desperate chance. But it was all that was left. He dropped down and let himself without even a splash into the water.

Arnold and Woodward took a step into the darkness, scarcely knowing what to expect, their eyes a bit better accustomed to the dusk. But if they had been there an hour, in all probability they could not have seen what was at their very feet.

Del Mar had sunk and was swimming under water in the swift black current sweeping under them. As they entered, he pa.s.sed out, nerved up to desperation.

Down the stream, just before it took its final plunge to the power wheel, Del Mar managed by a superhuman effort to reach out and grasp a wooden support of the flooring again and pull himself out of the stream. Smiling grimly to himself, he hurried up the bank.

"Some one's coming," whispered Price. "Get ready."

We levelled our guns. I was about to fire.