As if in answer to his words, there was a knock at the door and as Tom opened it a colored boy handed him an envelope which he instantly recognized as a cable.

It was addressed to Mr. Pauling and as Tom’s father tore it open and glanced at its contents a strange expression swept over his face and he uttered a sharp ejaculation of surprise.

“Speak of angels, Henderson!” he remarked, as he passed the cable to his associate. “What do you think of that?”

“Well, I’ll be——” began Mr. Henderson as he hurriedly read the familiar cypher message, “Smernoff has escaped! Confound those fellows! Can’t they keep any one under lock and key? The second time too. Now there will be the devil to pay.”

“Yes, it’s regrettable,” agreed Mr. Pauling, “but I wouldn’t worry over him. The chances are they’ll get him again and I can’t see how it will be possible for him to reach his friends down here or even to communicate with them—with his submarine gone and his confederates arrested or dead. And we have all the information he could give us. No, I don’t think his escape will trouble us much in this undertaking. I’d hate to be in your shoes and in the States with him though. He’s sworn to ‘get’ you, Henderson, and he’s absolutely reckless and ruthless, as you know.”

“Gosh, he might come down here!” exclaimed Tom.

“Little chance of that,” his father assured him. “Every ship will be watched and don’t forget he has neither diving suit, radio nor undersea boat to help him. Besides he’ll find it a hard job to discover where we are. Don’t be nervous over him, boys.”

For several days nothing eventful occurred and the boys began to find time hanging heavily on their hands. Mr. Pauling would not consent to their taking a trip on a sponging vessel as they had hoped, for, as he pointed out, word from Rawlins might be received at any moment and there could be no delay. But the arrival of the mails from New York, bringing the latest radio news and radio periodicals, proved a godsend to the boys who had discovered that a tiny island the size of New Providence was somewhat limited in the interests it possessed for two go-ahead, strenuous lads, despite its picturesque town, its odd people and its beauties.

The two were soon deep in the latest developments of radio and were eagerly discussing plans for the wonderful things they would do when the present trip was successfully ended and they were once more in New York. Tom was just reading an article on the almost miraculous properties of specially prepared crystals of Rochelle salt when his father entered the room.

“Better pack your duds!” he exclaimed. “Here’s good news for you.”

“Oh, I bet Mr. Rawlins’s arrived!” cried Tom, throwing aside his magazine and jumping up.

“Right the first time!” his father replied, smiling. “That is, he has not arrived, but I have just received a radio message from Disbrow saying ‘William sends regards’ which means that the submarine has signaled and that all is well. He is probably close to the prearranged meeting place now and the launch is ready. Get your things together and we’ll be off. Remember, if any one questions you we are off for a fishing trip.”

Half an hour later the four were aboard a fast cabin launch which had been purchased and held in readiness for the news of Rawlins’ arrival.

Leaving Nassau astern, the launch was headed towards the north, but no sooner were they out of sight of any prying eyes which might be watching from the island, than they slipped behind some low cays and shifted their course to the east. At the wheel was a stalwart brown-skinned young man and Tom in whispers asked his father if he was sure the negro could be trusted.

Mr. Pauling laughed. “You’re getting as suspicious of every one as an old hand,” he replied. “Don’t fret over Sam, Tom. He’s been with us for years and very luckily too. He was born and bred in the Bahamas and these natives never forget a channel or a reef. He was with me when I was down here in the spring.”

“But I never saw him before,” said Tom, rather puzzled to know where this chocolate-colored addition to their forces had been hidden.

“Of course not,” chuckled his father, “and you never saw several other men in Nassau whom I might name. I might add another sentence to that excellent motto of yours and that is: ‘and be seen by no one until occasion calls for it.’ However, Sam saw you and was never very far from you. In fact I believe he once taught you that living corals are not white.”

“Jehoshaphat!” exclaimed Frank. “You don’t mean to say he’s the boatman!”

“Exactly!” replied Mr. Pauling. “Didn’t you recognize him?”

“But, but, the boatman didn’t look like him,” declared Tom, staring at the pilot, “he had a gray beard and gray hair and talked like one of the Conchs.”

“A little gray wool and a gray wig will work wonders—especially on a black man,” replied Mr. Pauling. “And remember Sam is a Conch as you call them and can naturally talk his native dialect.”

“Well, I never believed all those detective stories about men disguising themselves,” said Frank, “but I will hereafter.”

Mr. Henderson laughed heartily. “No real detective or Secret Service man uses disguises—that is false beards and wigs and make up—nowadays,” he declared. “To attempt a disguise would be to excite suspicions at once—any crook with half an eye would penetrate such makeshifts in New York; but with a colored man down here it’s different. The natives are not observant and there are few if any skillful crooks, and who would imagine for a moment that a negro was in the Service? No, boys, you must learn to believe only what you actually see.”

“Even less than that,” added Mr. Pauling. “I should say ‘believe only half that you see and nothing you hear.’”

“Then I only believe half of Sam and nothing he told us,” laughed Tom. “Did he really work for Mr. Rawlins?”

“Yes and no,” replied his father. “He met Rawlins when I did last spring and did take a part in one film—Rawlins wanted a man to tackle a shark under water and Sam volunteered; but he was not regularly employed.”

“Gosh, then Sam really has done that!” cried Frank. “Say, I hope we see a shark so he can do it for us.”

“Sam has other matters to attend to,” Mr. Pauling reminded him, “but if he has time when we reach the place we’re bound for he will no doubt gladly accommodate you and any sharks that may be about.”

Now that the boys knew the secret of the black man they decided to have some sport themselves and after securing Mr. Pauling’s and Mr. Henderson’s promises that they would not tell Sam that the boys knew that he was their former boatman, the two lads plied Sam with questions, pretending to swallow everything he said without hesitation. Then, very adroitly, they led the conversation into other channels and let out many hints that led Sam to believe they had penetrated his former disguise.

“What do you dye your hair with?” asked Frank innocently. “It used to be gray.”

Sam looked troubled. “Dye ma hair?” he replied, striving to maintain a puzzled expression and to speak in casual tones. “I guess you is jokin’. Ah don’t dye ma hair, Boss. No, sir, ma wool’s jus’ as the Lord made it.”

“Well why did you shave off your whiskers?” asked Tom. “Thought you looked too old to suit those darky girls in Nassau?”

Sam was now genuinely uneasy. “Ah doan’ bother wif she,” he declared indignantly, and unconsciously lapsing into the Conch vernacular. “Ah always shaves. Yaas, sir, Ah never grow no whiskers. Wha’ fo’ yo’ arsk such interrogation, Chief?”

“I guess a shark must have bitten it off,” suggested Frank in an undertone nudging Tom slyly, “or perhaps it was in the way when he dove after corals to show to some other Northerners looking for white corals.”

Sam turned and stared at the boys in amazement. “Lawd bless yo’!” he exclaimed. “Den fo’ a fac’ yo’ knowed me an’ was jus’ pretendin’ yo’ didn’t all tha’ time!”

“Of course!” replied Tom trying to keep a sober face as he saw Sam’s surprise and chagrin at having been discovered, “you must have thought we were green.”

For a moment, poor Sam seemed utterly dispirited. He had taken the utmost pride in his clever disguise and now, after all, these two boys had penetrated it. If that were so, then no doubt, others had done the same and Mr. Pauling and Mr. Henderson would blame him.

But the next instant a relieved look swept over his good-matured face as he caught sight of the two gentlemen trying to stifle their laughs, and, realizing it had all been a plant, he burst into a hearty roar of merriment over the way he had been fooled.

“Ah guess yo’ young gent’men did sure 'nough get ma goat!” he exclaimed, “an’ Ah’m jus’ boun’ fo’ to get yours an’ knife a sh’ak.”

Now that the boys had had their sport with Sam they found him a most interesting companion, and standing in the bows of the speeding launch, asked him innumerable questions about the various islets, the birds, the fish and the reefs they passed. It was nearly sundown when they sighted the island where it had been agreed they would meet Rawlins—a lovely palm-fringed islet with silvery-white beaches, and, much to the boys’ surprise, they saw the roofs of buildings peeping from among the foliage.

“Why, people live there!” cried Tom. “Say, we can’t meet Mr. Rawlins there.”

“Those are Rawlins’ buildings,” replied his father smiling at Tom’s distressed expression. “Didn’t I tell you? This is where he takes his undersea pictures—his studio and workshop, you know—but at this season it’s deserted. We’re perfectly safe there.”

A few minutes later the launch slipped through a narrow channel between outjutting ledges of jagged, gray coral rock and entered a beautiful little harbor or cove. On one side was a low point, covered with coconut palms, and on the other a white sand-beach with a small dock and with a large wooden building,—red roofed and with green shutters—just beyond.

“Well we’re here first,” exclaimed Tom as the launch forged slowly towards the dock. “There’s no sign of the submarine.”

“No, but some one’s here!” cried Frank.

As he spoke a figure appeared upon the dock holding glasses to his eyes and the next moment the boys recognized it.

“Gosh! It’s Mr. Rawlins!” shouted Tom. “But where is the submarine?”

A moment later the launch grated alongside the pier and Rawlins with a grin welcomed them.

“But—but, where’s the submarine?” demanded Tom before Rawlins could speak.

“Safe and sound!” he replied. “Welcome to my kingdom!”

Then, when the first greeting was over, he exclaimed. “I’ll say I’ve news for you! Couldn’t guess what ’tis. When we were tinkering around in that old sub, we found a secret compartment—sort of locker—and some darned queer things in it—radio stuff of some sort, I expect. I didn’t show it to any one—not even to our ‘Sparks’ but I’ve got it up at the house. Come on and have a look at it. And I’ve another surprise for you too—but that will keep—that’s for you, Mr. Pauling. Come along.”

Hurrying up the path between the hedges of gay-flowered hibiscus the party entered the building which served Rawlins as den, living place and workshop combined.

The boys were amazed as they glanced about. They had not expected to find anything on the island and here they were surrounded with every comfort. Luxurious wicker-work furniture all about; enlarged photographs-and paintings of scenes from Rawlins’ sub sea films on the walls; rugs of woven grass and matting on the polished floors; a phonograph in one corner and shelves of books.

On a stand at one side of the room was a model of a submarine complete in all its details; there were models of sailing vessels on shelves and freshly cut flowers filled vases and bowls.

“Say, you’ve a regular house here!” cried Tom, “It’s fine!”

“Oh, it’ll do for a hang-out,” replied Rawlins as he began to undo a package, “But you’ll like the studio better. Look here, what do you make of these?”

As he spoke he showed the boys the contents of the package. There were one or two of the single control coils the boys had already seen, a pair of peculiar phone receivers, several beautiful shining crystals, one of which was secured in a metallic stand or ring and an odd affair about two feet in length and three inches in diameter looking like an overgrown walking stick wound with wire and with a sliding ring upon it.

For an instant, the two boys gazed at the collection with puzzled, uncomprehending faces and then, suddenly, a queer look of mingled surprise, delight and understanding swept across Tom’s features.

“Gosh!” he cried, picking up one of the crystals, “Gosh! I’ll bet I do know what these are. Say, they’re those wonderful Rochelle salt crystals I was reading about. Now we will have something worth while! But I can’t imagine what this thing is, it looks like a funny big coil, but whoever saw a coil like it and with this sliding ring on it?”

It was now Frank’s turn to exhibit his knowledge of the latest discoveries in radio. “Hurrah, I know!” he exclaimed. “It’s a resonance coil! Don’t you remember, I was just speaking about it when your father told us to get ready? Say, these things beat loop aerials all to pieces. Why, that magazine said that with one of ’em you could tell where a sending station was and even how far away! It’s an aerial and tuning coil in one. Gee, Tom, we are in luck! If we want to find those chaps now we’ll have a regular cinch!”

At the boys’ excited exclamations Mr. Henderson, who had been examining a picture, turned to them.

“What’s all the excitement, boys?” he asked. “Anything interesting that Rawlins has found?”

“Well I should say so!” declared Tom. “Look, here’s some of those Rochelle salt crystals and a resonance coil. Do you know about them, Mr. Henderson?”

“Jove, you’re right!” ejaculated the other. “Yes, I’ve seen experiments made with the salt—and have seen them used in submarine work during the war too, and I’ve read Gen. Squiers’ articles on the resonance coil and its properties. No wonder those fellows in the sub got by with such things to aid them.”

“Well I suppose it’s all mighty plain to you, but I’ll be hanged if I can see where Rochelle salts come in,” declared Rawlins. “I thought that was medicine.”

“So it is, under certain conditions,” agreed Mr. Henderson, “but if the salt is prepared or ‘grown’ so as to form a certain kind of crystal it possesses almost magical properties. By its aid one can hear a fly walk, insects talk or molecules of metal turning over in an iron bar.”

“Nothing doing!” exclaimed Rawlins. “I can believe pretty big yarns after seeing what radio does, but I’m from Missouri when you talk about a bit of salt making a fellow hear a fly’s trotters or the inside of iron getting restless. You’ll have to show me.”

“That will be easy, I imagine,” replied Mr. Henderson. “Tom says he’s been reading the accounts of it. I expect he can make you hear your own thoughts almost. But with no exaggeration it is a most marvelous thing. During the war we used it as a detector to hear vessels at a distance—particularly subs, and it saved countless thousands of lives. One man in Washington is employed to devote all of his spare time merely to growing these special crystals. If Tom can arrange the apparatus on the submarine we can locate the other sub if we get near her. You’ve made a great find, Rawlins.”

“What’s that you said about another sub?” asked Rawlins. “Don’t tell me they’ve got another one!”

“That’s what we think,” replied Mr. Pauling. “I forgot you didn’t know.” In a few words he related Commander West’s story of the finding of the deserted schooner and the disappearance of the crew.

“I’ll say they’re some little deserters!” exclaimed Rawlins, “and you’re dead right about another sub, I’ll bet. And say, that helps us some too. They left that schooner and took to the U-boat—that is if they did have a sub at the Caicos. Well, that fits right in with my theory about the latitude and longitude. If they left the schooner there and took the sub you can bet the Caicos are not far from their hang-out. I’ll bet they knew the destroyer wouldn’t touch the smack and expected to lie low and take her again after the boys had cleared out. Why, they might have been lying submerged right alongside of her or with their periscope sticking up watching the destroyer from back of some reef or a bunch of mangroves. Yes, sir—if we hit the Caicos we won’t be far off.”

“H-m-m, there’s a lot of good reasoning there,” agreed Mr. Pauling. “And if we’re to prove the theory the quicker we get started the better.”

“Right you are,” agreed Rawlins. “We’re ready to sail any time. I just want to get a few things together and I’ll be with you. Want to have a look around the studio and shop, boys?”

The boys would gladly have remained for hours or even days in the studio but they realized there was no time to be lost. Here were diving suits of all kinds, sets representing the interior of ships and submarines, the yards and rigging of a bark complete, but with no hull, strange devices at whose use they could only guess and in one corner the enormous intricate octopus of rubber, springs and wire which when occupied by a man, could be made to imitate so perfectly the real creature that scientists who had seen the picture in which it figured had insisted that it was a genuine octopus.

The workshop also was full of interesting things. Here was where Rawlins and his assistants made the diving suits, the under-sea apparatus for taking the films, the lifelike octopus, the miniature ships, the complicated and wonderful counterfeits of the interiors of the submarines and many other objects.

But long before they had half time to examine all these things Rawlins was ready and leading the way along a narrow path through the brush headed for the other end of the island.

“Aren’t you afraid some one will disturb your property?” asked Mr. Henderson, “I shouldn’t think it safe to leave all these things unguarded.”

“I don’t,” replied Rawlins. “I have an old colored chap and his wife who live here. That’s why I kept the submarine out of sight.”

“Where are they now?” asked Mr. Pauling. “Are you sure their curiosity won’t be aroused and that they may not wonder at your sudden appearance and departure and our arrival?”

Rawlins laughed. “They might be curious or talk about a sub—if they saw it, but as far as I’m concerned they are quite sure I’m an obeah man—sort of witch-doctor you know—and absolutely incomprehensible. If I dropped from the sky in a parachute and left in a pillar of flame they’d think it quite in keeping with my habits and no more remarkable than walking into the sea and out again at will. Just at present they’re so busy over some things I brought ’em that they wouldn’t see a sub if it poked its nose into their cabin. And even if they wanted to talk they couldn’t, there’s not a soul living within a dozen miles.”

They had now come out of the brush upon a second miniature harbor where a small boat was drawn up on the smooth beach.

With Sam helping, Rawlins shoved off the boat as the others climbed in.

“We might have come around by the launch, I suppose,” Rawlins remarked, “but it’s safer over at the dock and this boat’s handier.”

Sam at the oars and Rawlins steering, the boat swept away from the beach and headed for a jutting point.

As they drew near and the boys were watching the circling seabirds and admiring the beautifully colored water, Rawlins spoke to Sam and ordered him to stop rowing.

“See anything of the sub?” he asked as the boat lost headway.

Every one gazed about, expecting to see the undersea boat just awash or just emerging from the surface, but not a ripple broke the glassy water. Along the shore they were approaching was a dense belt of green trees—mangroves and sea grape—with a few ragged coconut palms above all, but not a sign of anything remotely resembling a submarine.

“No, I give up,” said Mr. Pauling at last.

“So do I,” added Mr. Henderson.

“Me too,” said Tom.

“I don’t believe it’s here,” declared Frank.

Rawlins chuckled. “Thought it was pretty good,” he exclaimed. “You’ve been looking right at her, too.”

“Looking at her!” exclaimed Mr. Pauling.

“Where?”

“Straight ahead,” laughed Rawlins, “over against that point.”

All eyes were now turned towards the point and as Sam again took to his oars and they drew nearer and nearer the two men and the boys searched the rocks and greenery in vain.

Not until they were within one hundred yards of the shore were they rewarded. Then Tom uttered a cry. “Hurrah, I see it!” he shouted. “Gosh, but she was hidden! Say, how did you do it?”

“Just a bit of camouflage,” chuckled Rawlins. “Idea I got when making a set once. Thought it might be handy to be able to lie on the surface and not be seen sometime.”

“Well you’ve certainly succeeded,” declared Mr. Henderson. “The effect of the rocks and foliage is perfect. I’d defy any one to see her five hundred feet distant.”

Even now the outlines of the submarine were so hidden by the clever painting on her upper works and hull that the boys could not have been sure what was boat and what was foliage if a man had not appeared, emerging from a hatchway, and followed by two others.

The next minute the boat was alongside the craft, and scrambling onto her decks the boys gazed about with interest.

They had been on this same underseas boat before, but then she had been tied up to a dock in the Navy Yard and only curiosity to see what she contained had filled their minds. But now she was riding on the waters in the West Indies, she was manned and ready to sail and the boys were wildly excited at the thoughts of adventures to come and of sailing on a real submarine under the sea.