Rather alarmed at the strange disappearance of Elaine after I brought her home, I had started out along the road to the sh.o.r.e to look for her, thinking that she might perhaps have returned there.

As I walked along a young tough--at least at the time I thought it was a young tough, so good was the disguise she had a.s.sumed and so well did she carry it off--slouched past me.

What such a character could be doing in the neighborhood I could not see. But he was so noticeably tough that I turned and looked. He kept his eyes averted as if afraid of being recognized.

"Great Caesar," I muttered to myself, "that's a roughneck. This place is sure getting to be a hang-out for gunmen."

I shrugged my shoulders and continued my walk. It was no business of mine. Finding no trace of Elaine, I returned to the house. Aunt Josephine was in the library, alone.

"Where's Elaine?" I asked anxiously.

"I don't know," she replied. "I don't think she's at home."

"Well, I can't find her anywhere," I frowned wandering out at a loss what to do, and thrusting my hands deep in my pockets as an aid to thought.

Somehow, I felt, I didn't seem to get on well as a detective without Kennedy. Yet, so far, a kind providence seemed to have watched over us.

Was it because we were children--or--I rejected that alternative.

Walking along leisurely I made my way down to the sh.o.r.e. At a bridge that crossed a rather turbulent stream as it tumbled its way toward the sea, I paused and looked at the water reflectively.

Suddenly my vagrant interest was aroused. Up the stream I saw some one struggling in the water and shouting for help as the current carried her along, screaming.

It was Elaine. The hat and mustache of her disguise were gone and her beautiful t.i.tian hair was spread out on the water as it carried her now this way, now that, while she struck out with all her strength to keep afloat. I did not stop to think how or why she was there. I swung over the bridge rail, stripping off my coat, ready to dive. On she came with the swift current to the bridge. As she approached I dived. It was not a minute too soon. In her struggles she had become thoroughly exhausted. She was a good swimmer but the fight with nature was unequal.

I reached her in a second or so and took her hand. Half pulling, half shoving her, I struck out for the sh.o.r.e. We managed to make it together where the current was not quite so strong and climbed safely up a rock.

Elaine sank down, choking and gasping, not unconscious but pretty much all in and exhausted. I looked at her in amazement. She was the tough character I had just seen.

"Why, where in the world did you get those togs?" I queried.

"Never mind my clothes, Walter," she gasped. "Take me home for some dry ones. I have a clue."

She rose, determined to shake off the effects of her recent plunge and went toward the house. As I helped her she related breathlessly what she has just seen.

Meanwhile, back of that wall of water, the wireless operator in the cave was sending the messages which Del Mar's emissary dictated to him, one after another.

With the high resistance receiving apparatus over his head, Arnold was listening to the wireless signals that came over his "radio detective"

on the yacht, moving the slider back and forth on a sort of tuning coil, as he listened. Woodward stood close beside him.

"As you know," Arnold remarked, "by the use of an aerial, messages may be easily received from any number of stations. Laws, rules, and regulations may be adopted by the government to shut out interlopers and to plug busybody ears, but the greater part of whatever is transmitted by the Hertzian waves can be s.n.a.t.c.hed down by this wireless detective of mine. Here I can sit in my wireless room with this ear-phone clamped over my head drinking in news, plucking the secrets of others from the sky--in other words, this is eavesdropping by a wireless wire-tapper."

"Are you getting anything now?" asked Woodward.

Arnold nodded, as he seized a pencil and started to write. The lieutenant bent forward in tense interest. Finally Arnold read what he had written and with a peculiar, quiet smile handed it over. Woodward read. It was a senseless jumble of dots and dashes of the Morse code but, although he was familiar with the code, he could make nothing out of it.

"It's the Morse code all right," he said, handing it back with a puzzled look, "but it doesn't make any sense."

Arnold smiled again, took the paper, and without a word wrote on it some more. Then he handed it back to Woodward. "An old trick," he said.

"Reverse the dots and dashes and see what you get."

Woodward looked at it, as Arnold had reversed it and his face lighted up.

"Harbor successfully mined," he quoted in surprise.

"I'll show you another thing about this radio detective of mine," went on Arnold energetically. "It's not only a wave length measurer, but by a process of my own I can determine approximately the distance between the sending and the receiving points of a message."

He attached another, smaller machine to the wireless detector. In the face was a moving finger which swung over a dial marked off in miles from one upward. As Arnold adjusted the new detector, the hand began to move slowly. Woodward looked eagerly. It did not move far, but came to rest above the figure "2."

"Not so very far away, you see, Lieutenant," remarked Arnold, pointing at the dial face.

He seized his gla.s.s and hurried to the deck, levelling it at the sh.o.r.e, leaning far over the rail in his eagerness. As he swept the sh.o.r.e, he stopped suddenly. There was a house-roof among the trees with a wireless aerial fastened to the chimney, but not quite concealed by the dense foliage.

"Look," he cried to Woodward, with an exclamation of satisfaction, handing over the gla.s.s.

Woodward looked. "A secret wireless station, all right," he agreed, lowering the gla.s.s after a long look.

"We'd better get over there right away," planned Arnold, leading the way to the ladder over the side of the yacht and calling to the sailor who had managed the little motor-boat to follow him.

Quickly they skimmed across to the sh.o.r.e. "I think we'd better send to the Fort for some men," considered Arnold as they landed. "We may need reinforcements before we get through."

Woodward nodded and Arnold hastily wrote a note on a rather large sc.r.a.p of paper which he happened to have in his pocket.

"Take this to Colonel Swift at Fort Dale," he directed the sailor. "And hurry!"

The sailor loped off, half on a run, as Arnold and Woodward left down the sh.o.r.e, proceeding carefully.

At top speed, Arnold's sailor made his way to Fort Dale and was directed by the sentry to Colonel Swift who was standing before the headquarters with several officers.

"A message from Lieutenant Woodward and Professor Arnold," he announced, approaching the commanding officer and handing him the note.

Colonel Swift tore it open and read:

Have located radio aerial in the woods along sh.o.r.e. Please send squad of men with bearer.--ARNOLD.

"You just left them?" queried the Colonel.

"Yes sir," replied the sailor. "We came ash.o.r.e in his boat. I don't know exactly where they went but I know the direction and we can catch up with them easily if we hurry, sir."

The colonel handed the note quickly to a cavalry officer beside him who read it, saluted at the orders that followed, turned and strode off, hastily stuffing the paper in his belt, as the sailor went, too.

Meanwhile, Del Mar's valet was leaving the bungalow and walking down the road on an errand for his master. Up the road he heard the clatter of hoofs. He stepped back off the road and from his covert he could see a squad of cavalry headed by the captain and a sailor cantering past.

The captain turned in the saddle to speak to the sailor, who rode like a horse marine, and as he did so, the turning of his body loosened a paper which he had stuffed quickly into his belt. It fell to the ground. In their hurry the troop, close behind, rode over it. But it did not escape the quick eye of Del Mar's valet.

They had scarcely disappeared around a bend in the road when he stepped out and pounced on the paper, reading it eagerly. Every line of his face showed fear as he turned and ran back to the bungalow.

"See what I found," he cried breathlessly bursting in on Del Mar who was seated at his desk, having returned from the harbor.