Some of the men were down below in its path. But the onrushing cable car was too much for them. They could only leap aside to save themselves.

On down the incline, gathering momentum every second, the car dashed, Del Mar swaying crazily but keeping his footing. We followed as fast as we could, but it was useless.

Out on the wharf it sped at a terrific pace. At the end it literally catapulted itself into the water, crashing from the end of the pier. As it did so, Del Mar gave a flying leap out into the harbor, struck the water with a clean dive and disappeared.

On down the hill we hurried. There in the water was Del Mar swimming rapidly. Almost before we knew it, we saw him raise his hand and signal, shouting.

There only a few yards away was the periscope of a submarine. As we watched, we could see that it had seen him, had turned in his direction. Would they get him?

We watched, fascinated. Some of our men fired, as accurately as they could at a figure bobbing so uncertainly on the water.

Meanwhile the submarine approached closer and rose a bit so that the hatchway cleared the waves. It opened. One of the foreign agents a.s.sisted Del Mar in.

He had escaped at last!

It was most heart-breaking to have had Del Mar so nearly in our grasp and then to have lost him. We looked from one to another, in despair.

Only Arnold, in his disguise as a hermit, seemed undiscouraged.

Suddenly he turned to Woodward.

"What time is it?" he asked eagerly.

"A little past noon."

"The Kennedy wireless torpedo!" he exclaimed. "It arrived to-day.

Burnside is trying it out."

Suddenly there flashed over me the recollection of the marvellous invention that Kennedy had made for the Government just before his disappearance, as well as the memory of the experience I had had once with the intrepid Burnside.

Woodward's face showed a ray of interest and hope in the overwhelming gloom that had settled on us all.

"You and Jameson go to Fort Dale, quick," directed Arnold eagerly. "I'm not fit. Get Burnside. Have him bring the torpedo in the air-boat."

We needed no further urging. It was a slender chance. But I reflected that the submarine could not run through the bay totally submerged. It must have its periscope in view. We hurried away, leaving Arnold, who slowly mounted the hill again.

How we did it, I don't know, but we managed to get to the Fort in record time. There near the aeroplane hangar, sure enough, was Burnside with some other men adjusting the first real wireless Kennedy torpedo, the last word in scientific warfare, making an aerial torpedo-boat.

We ran up to the hangar calling to Burnside excitedly. It was only a moment later, that he began to issue orders in his sharp staccato. His men swarmed forward and took the torpedo from the spot where they had been examining it, adjusting it now beneath the hydroaeroplane.

"Jameson, you come with me," he asked. "You went before."

We rose quickly from the surface and planed along out over the harbor.

Far off we could see the ripple from the periscope of the submarine that was bearing Del Mar away. Would Kennedy's invention for which Del Mar had dared so much in the first place prove his final undoing? We sped ahead.

Down below in the submersible Del Mar was giving hasty orders to his men, to dip down as soon as all the shipping and the sand bars were cleared.

I strained my eyes through the gla.s.ses reporting feverishly to Burnside what I saw so that he could steer his course.

"There it is," I urged. "Keep on--just to the left."

"I see it," returned Burnside a moment later catching with his naked eye the thin line of foam on the water left by the periscope. "Would you mind getting that torpedo ready?" he continued. "I'll tell you just what to do. They'll try to duck as soon as they see us, but it won't be any use. They can't get totally submerged fast enough."

Following Burnside's directions I adjusted the firing apparatus of the torpedo.

"Let it go!" shouted Burnside.

I did so, as he volplaned down almost to the water. The torpedo fell, sank, bobbed up, then ran along just tinder the surface. Already I was somewhat familiar with the wireless device that controlled it, so that while Burnside steadied the aircraft I could direct it, as he coached me.

The submarine saw it coming now. But it was too late. It could not turn; it could not submerge in time.

A terrific explosion followed as the torpedo came in contact with the boat, throwing a column of water high in the air. A yawning hole was blown in the very side of the submarine. One could see the water rush in.

Inside, Del Mar and his men were now panic-stricken. Some of them desperately tried to plug the hole. But it was hopeless. Others fell, fainting, from the poisonous gases that were developed.

Of them all, Del Mar's was the only cool head.

He realized that all was over. There was nothing left to do but what other submarine heroes had done in better causes. He seized a piece of paper and hastily wrote:

Tell my emperor I failed only because Craig Kennedy was against me.--DEL MAR.

He had barely time to place the message in a metal float near-by. Down the submarine, now full of water, sank.

With his last strength he flung the message clear of the wreckage as it settled on the mud on the bottom of the bay.

Burnside and I could but stare in grim satisfaction at the end of the enemy of ourselves and our country.

Up the hillside plodded Professor Arnold still in his wild disguise as the hermit. Now and then he turned and cast an anxious glance out over the bay at the fast disappearing periscope of the submarine.

Once he paused. That was when he saw the hydroaeroplane with Burnside and myself carrying the wireless torpedo.

Again he paused as he plodded up, this time with a gasp, of extreme satisfaction. He has seen the water-spout and heard the explosion that marked the debacle of Del Mar.

The torpedo had worked. The most dangerous foreign agent of the coalition of America's enemies was dead, and his secrets had gone with him to the bottom of the sea. Perhaps no one would ever know what the nation had been spared.

He did not pause long, now. More eagerly he plodded up the hill, until he came to the hut.

He pushed open the door. There lay Elaine, still bound. Quickly he cut the cords and tore the gag from her mouth.

As he did so, his own beard fell off. He was no longer the hermit. Nor was he what I myself had thought him, Arnold.

"Craig!" cried Elaine in eager surprise.

Kennedy said not a word as he grasped her two hands.

"And you were always around us, protecting Walter and me," she half laughed, half cried hysterically. "I knew it--I knew it!"