Henry watched Tom’s head disappear, he saw the little silvery bubbles rising, for an instant he could distinguish the darker shadow in the water which marked his friend, and then nothing but the rippling green surface of the river was visible through the open trapdoor in the floor of the dock. He and Frank were alone, Tom and Rawlins were beneath the river, and yet, down there at the bottom of the gurgling water, the unseen two could hear every word spoken in the room above. It was marvelous, fantastic and almost incredible. But even more wonderful and impossible events were about to take place. Frank had already heard Tom’s parting words over the set, although not a sound had issued from his helmet, and now, with the others under the water, Frank was again talking.

“Yes, I can hear you finely,” he said. “Say, it’s wonderful. Where are you? Right under the dock? I’m going to let Henry talk to you. I feel as if I were dreaming!”

As Henry listened at the set and Tom’s words came to his ears he actually jumped, for he had never expected the words to come as plainly and distinctly as if Tom had been in the room with him and talking to him direct.

“That you, Henry?” came Tom’s voice. “Gee, but it’s great. I can hear you just as well as if I were up there. Does my voice sound loud?”

“Loud as if you were standing alongside of me,” Henry assured him. “I can’t believe you’re really under water.”

So, for some time, the three boys and Rawlins conversed, chatting and laughing, expressing their wonder and delight in boyish expletives and overjoyed at finding their plans and their work had proved such an immense success.

“We’re going off a ways,” announced Tom, at last. “Mr. Rawlins wants to find out how far away we can hear and send. We’re going to walk down the river. You keep talking and after we’ve gone a few hundred yards we’ll call you. If you don’t reply that you heard us we’ll keep walking back and trying until you do get us. Then we’ll know our range.”

For a time, the two boys on the dock kept up a steady conversation with Tom and Rawlins, and, much to their surprise, the sounds of their friends’ voices continued as loud as when they were directly under the dock.

“It’s a funny thing,” remarked Frank during a lull in the under-sea conversation, “I thought they’d get out of range very soon. I never would have believed that these little fifty-meter waves could carry that far with only a two-foot grid for an aËrial. The water must be a heap better for waves than the air.”

Then there was an interval when no sounds came in and Frank was about to call to Tom when, to his ears, came a suppressed “Wha—wha” followed by a hoarse “Sssh!”

Whether Rawlins had intended this for Tom or himself Frank did not know, but he decided that, for some unknown reason, the diver wished silence and so wisely refrained from speaking.

“I would like to know what Mr. Rawlins wanted to be quiet for,” said Frank, holding his hand over the mouthpiece of his microphone. “But I suppose there’s some good reason for it.”

Scarcely had he ceased speaking when he was startled by a sharp exclamation of surprise from Tom.

So unexpected was it that Frank responded involuntarily. “What’s that you said?” he asked, exactly as though Tom had been there in the room. But there was no audible reply, merely some faint sounds like subdued whispers, followed by silence.

“Gee, there’s something mighty funny going on!” exclaimed Frank, addressing Henry. “Tom said ‘Gosh’ something and then, when I answer he doesn’t say a thing—just some little sounds like whispers. Say, I do wonder what they’re up to!”

“Oh, I expect they’re trying to see if they can talk together without your hearing them,” suggested Henry. “Probably that’s why Mr. Rawlins told you to be quiet.”

“Well, I’m going to find out,” declared Frank. “They’ve no right to keep us wondering like this.”

“Hello!” he cried into the microphone. “What on earth’s the matter? I haven’t heard a word from you two for five minutes. Can you hear me?”

But instead of Tom’s voice in reply Frank was amazed to hear thick, guttural words rapidly spoken, and among them he made out only one that he understood, the name “Oleander.”

“Henry!” exclaimed Frank, speaking in hushed tones as if he feared being overheard, “Henry, there’s that fellow talking again—the one you and Mr. Rawlins heard—talking in Dutch or something!”

Then the strange voices ceased and very faintly and indistinctly Frank heard Tom’s voice asking,

“What does it mean?”

Frank was puzzled. “What does what mean?” he inquired into the microphone. But the reply, if Tom made one, was drowned out and confused by Rawlins’ voice. Frank could not distinguish all the words, but he knew from the sounds and intonations that Tom and the diver were discussing some matter between them and he refrained from interrupting.

Then the voices ceased and Frank called, begging Tom to explain matters, asking if anything was wrong. But for a moment there was no reply and he wondered if his voice could be heard.

Then to his ears came Tom’s familiar “Gosh!” a few unintelligible words and a shrill whistle, followed by Rawlins’ voice. Part of it Frank could not catch but as he strained his ears he distinctly heard Rawlins exclaim:

“We’re in a dangerous place! Come on. Let me go first!”

Frank’s face paled. “Jehoshaphat!” he exclaimed to Henry who, realizing that something mysterious was taking place beneath the river, was bending close. “Jehoshaphat! They’re in danger! Say, what can it be? Maybe they’re caught in quicksand or a current or under a boat.”

Pleadingly, with fright and worry expressed in his tones, Frank begged Tom to reply, to tell him what was wrong, what the danger was. For a space he waited anxiously for his chum’s reply and then, at last, it came.

“It’s all right,” called Tom. “Don’t worry. Stop talking and just listen!”

Frank turned to Henry and disconnected the microphone by throwing off a switch to make sure that no sound could be sent.

“I guess they’re all right,” he said. “But I’m worried just the same. Why should he want me to be quiet and just listen. Oh, I do wish they’d come back.”

“There’s those foreign words again,” he announced presently, “and, say—I didn’t think of it before—there are two talking now.”

Then followed silence, not a sound, not even a hum or buzz of interference greeted his ears and anxiously he listened, half fearful that some awful casualty had happened to Tom and Rawlins out there somewhere under the turbid waters of the river.

The moments passed terribly slowly to the two boys and then Frank again gave a start as he heard Tom ejaculate “Gosh!” followed by some rapid low-spoken words, only one of which Frank could catch—the word “wreck.”

“That’s it,” he announced to Henry with a sigh of relief. “They’ve found a wreck. Gee! perhaps they’ve found treasure.”

Henry laughed gayly. “Oh, that’s good!” he exclaimed. “Treasure in the East River! You must think you’re down in the West Indies or somewhere.”

“Well, I don’t see what’s so awful funny about finding a wreck or treasure in the East River,” declared Frank petulantly. “Lots of boats have sunk here and why shouldn’t one of ’em have treasure on it? I don’t mean millions of dollars worth of gold or jewels of course—like pirates’ treasure—but there might be a box of money or something.”

“You’re way off,” replied Henry. “They wouldn’t leave a wreck here for a week. They’d get it up or blow it up right away. Why, a wreck here would block the channel. No, sir, you heard ’em wrong.”

“I did not!” stoutly maintained Frank. “I know Tom said something about a wreck. I don’t care what you say. How do you know there isn’t some old wreck out there somewhere? It may have been there for years; how would any one know?”

“Why, Mr. Rawlins and Tom aren’t the only divers who ever went down here,” insisted Henry. “The city and the government and wrecking companies and contractors have divers going down all the time. I’ve watched ’em working heaps of times. Father’s a construction engineer and I know he always has divers at work around New York. Some of ’em would have found a wreck if it had been there.”

“Well, anyway we’ll know pretty soon,” said Frank. “They can’t stay down much longer. They must——”

With a startled cry his words ended and his scared, pale face told Henry that something dreadful had happened. Ringing in Frank’s ears, shrill, filled with deadly terror, the shriek of a boy frightened almost out of his senses, came Tom’s despairing cry—a wordless, awful scream.

“What’s the matter?” Frank forced his paralyzed tongue to form the words. “Tom! Oh, Tom! What’s wrong? Why did you yell?”

“Help! Send for help!” rang back the answer. “It’s awful”—followed by words so filled with mortal terror that Frank could make nothing of them and then—“Get Dad! Get the police!”

Frank waited to hear no more. Dropping the receivers he leaped across the room, jerked the receiver from the telephone and frantically called for Mr. Pauling’s number. But in his fright and terror, his fear for Tom, his hurried words were a mere jumble to the operator.

“Can’t hear you,” came the girl’s voice. “What number did you say?”

Again Frank yelled. “Watkins 6636!” he cried, striving to make his words clear.

“Watkins 3666?” inquired the girl, and Frank could almost hear her masticating gum.

“No, 6636!” he screamed. “Hurry!”

The seconds that followed seemed like years to Frank. Across his brain flashed a thousand fears and he suffered untold agonies as he stood there, sweat pouring from his face. What if Mr. Pauling should not be in his office? Suppose the line were busy? What if the girl got the wrong number? How slow she was! Had she forgotten the call? Would no one answer? And then, when he was sure he must have waited hours, his heart gave a great leap, a load seemed lifted from his mind as he heard Mr. Pauling’s cheery, deep-throated:

“Hello! Who is it?”

“It’s Frank!” fairly screamed the boy. “Tom’s in trouble! I don’t know what—he’s under the river—with Mr. Rawlins. He wants help! Sent for you! Wants police!”

Then, when at last Mr. Pauling had succeeded in grasping the message and in excited tones had shouted, “All right, I’ll be down instantly!” Frank sank limply to the floor.

But the next second he was up and at the table by the radio set.

“Have you heard anything?” he inquired anxiously of Henry, who had taken up the receivers and had been listening while Frank called Mr. Pauling.

“Not a word,” replied Henry.

“Oh, gosh! Oh, I do wish they’d hurry!” exclaimed Frank. “Oh, they’re terribly slow! And how will they get to him? How do we know where he is?”

Slowly the minutes dragged by. Each tick of the cheap clock on the table seemed to spell Tom’s fate and still no sound came from beneath the river. Once, Henry thought he caught a word, an exclamation half suppressed, but he could not be sure. He had called Tom, but no reply had come. Were the two dead? Had some awful calamity overtaken them at the bottom of the river? Was this to be the tragic end of all their experiments? Was Tom’s death the reward for their success?

Then, from far up the street, came the clamor of a bell, and the screech of a motor horn sounded from nearer at hand.

At the same instant Henry uttered a glad, joyous cry. “They’re all right!” he shouted. “I just heard Rawlins tell Tom to go ahead!”

With a quick motion, he threw in the switch and at that moment Frank’s ringing shout of joy filled the room.

But before Henry could call to Tom, before he could utter a sound, hurrying, tramping footsteps echoed from the dock, the door burst inwards with a bang and into the room leaped Mr. Pauling. Beside him was a heavy-jawed man with drawn pistol and over his shoulder through the open doorway the boys saw the visored caps and blue coats of police.

“They’re safe!” yelled Frank, trying to make his voice heard above the excited, shouted interrogations of Mr. Pauling. “We just heard them.”

Mr. Pauling leaped towards the open trapdoor, the police crowding at his heels. Henry dropped his instruments and joined them and all crowded forward.

A shadow seemed to hover in the dull water and a slender affair of wire broke the surface.

“They’re here!” screamed Frank.

“Thank God!” echoed Mr. Pauling fervently.

Hardly had the words of thankfulness left his lips when he uttered a startled cry, and, throwing himself face downward at the edge of the trapdoor, plunged his arms into the swirling water. The dim shadowy form of the diver whose helmet had just appeared, had swayed to one side; his hands, clutching the upper rungs of the ladder, had loosened their grasp, his arms had wavered and had taken a feeble stroke as if trying to swim and from the receiver on the table had issued a despairing cry, a choking, gurgling groan, ending in a gasp.

Whether the swaying, half-floating form was Tom or Rawlins, Mr. Pauling could not know, for in the suits identity was lost, but trained as he was through long years in a service where to act instinctively meant life or death, he instantly dropped to the floor and clutched at the dim figure beneath. Had he delayed for the fraction of a second he would have been too late, but, as it was, his fingers closed on one of the diver’s wrists. The next instant he had grasped the other arm and a moment later, with Henderson’s aid, he had dragged the dripping, limp form onto the dock and the two men were cutting the suit and helmet from the unconscious form. But they already knew it was Tom. The boy’s limbs projecting from the short tunic had proved this and Mr. Pauling’s face was white and strained as they dragged the khaki-colored garment and the helmet from his son.

“Thank Heaven Rawlins fixed those suits so he could not breathe flames!” exclaimed Mr. Henderson, as the helmet was drawn from Tom’s head. “He’s breathing, Pauling!”

As he spoke, there was a disturbance at the door and the police stood aside as an ambulance surgeon pushed his way hurriedly into the room. He bent over Tom in silence for an instant and then he glanced up and Mr. Pauling read good news in his eyes.

“Don’t worry!” he exclaimed. “He’s not hurt. Hasn’t breathed any water. Just in a faint, I think. He’ll be around in a moment. Hello! Here’s another!”

While he had been speaking, another helmeted form had appeared, dragging a limp figure, and, holding to the latter’s legs still another diver was climbing up the ladder.

“What the dickens!” exclaimed Mr. Henderson glancing up. “Who the devil are these? Two divers go down and four come up!”

Dropping the apparently lifeless diver on the floor Rawlins dragged off his helmet, glanced about in a puzzled way and then, without waiting to ask questions exclaimed, “Here, Doctor! Quick! Get at this chap!”

At his words, the doctor and his assistant sprang to the side of the form on the floor and rapidly stripped off his helmet and, as the man’s face was exposed, even the hardened surgeons could not restrain a gasp of horror and amazement. The face was horrible to look upon. It was scorched, seared, blackened, the eyebrows burned off, the eyelids hanging in shreds, the sightless eyes staring white and opaque like those of a boiled fish. Rawlins gave a single glance at him.

“Oh, Lord!” he ejaculated. “He’s done for! He’s had flames from the chemicals in his helmet! Poor devil, he must have suffered!”

Then, turning to Mr. Henderson, he exclaimed.

“Better get the suit off this other chap. Don’t know who he is, but he’s something rotten! Guess it’s a good thing the police are here.”

As Mr. Henderson and Rawlins stepped towards the man who still wore his suit, the fellow raised an arm and leaped, or tried to leap, away, quite forgetting the heavy, lead-soled boots he wore. The result was that he tripped and fell heavily and, before Rawlins or Henderson could reach him, he was twisting and rolling towards the gaping trapdoor. An instant more and he would have been in the water, but just as he reached the edge of the opening, Frank, who with Henry had been staring open-mouthed and dumbfounded at the surprising and incomprehensible events taking place so rapidly before them, sprang forward and slammed shut the door which, in falling, pinned the fellow’s legs beneath it. Then, as if fearing the man might wriggle free, the excited boy jumped upon the heavy planks. But there was no fight or attempt to escape left in the fellow and, as several policemen rushed forward and seized him, he submitted without the least resistance and a moment later had been stripped of his suit.

Once more it was Mr. Henderson’s turn to be amazed, for, as he caught sight of the man’s face, as he saw the closely-cropped, bullet-shaped head, the tiny, close-set piggish eyes and the big loose-lipped mouth he could scarcely believe his eyes and uttered a sharp exclamation of wonder.

“Put the bracelets on him and don’t give him a chance!” he ordered the police and, as the shining irons snapped with a click about the man’s wrists and the officers led him to one side, the small piglike eyes glared at Mr. Henderson with such mingled hatred, brutality and ferocity that the boys shivered.

Rawlins was now bending above Tom beside Mr. Pauling and when, a moment later, the boy took a long, deep breath and his eyes fluttered open, the anxious, strained expression upon the diver’s face vanished.

“I’ll say he’s a good sport!” he ejaculated. “Poor kid! Don’t wonder he went clean off! And he saved my life too—with his under-sea radio at that!”