Rob, in his place of concealment, could hear the two men talking as they rowed.

Their conversation related, in the main, to the affairs of the night. Apparently, so far as Rob could gather, the stealing of the plans of the submarine was not yet complete. It appeared that Barton was to remain on the island in his capacity as trusted aide to Mr. Barr, and to gather up all he could of the details of the new submarine, down to the smallest particular.

Scarcely daring to breathe, Rob listened with all his might to the conversation of the oarsmen.

At the same time the thought was running through his mind that he had acted rashly in taking the step he had. But the boy pluckily made up his mind to stick to his resolution of discovering just what was going on inimical to the plans of the United States Government and Mr. Barr.

Before very long the prow of the boat grated on a sandy beach, and the two men, gathering up some rolls of paper and several bulky-looking objects, left the craft, first securing it by an anchor and line.

As their footsteps died away, Rob ventured to raise his head above the gunwale of the boat and follow them with his eyes. He saw them ascend the beach and enter the hut, apparently a structure once used by fishermen or hunters.

After an interval a light shone from the solitary window of the hut, and Rob came to a sudden resolve to find out just what was going forward. With this object in view he clambered out of the boat, taking every precaution against making unnecessary noise. On hands and knees he then approached the lighted window.

The night was dark, and, standing at a fair distance from the casement, he did not feel much fear of being seen from within. It is hard for persons in a brightly lighted chamber to perceive what is going on outside.

Seated around a rough table in the hut, which consisted of only one room, Rob saw three men. Two of them, undoubtedly, were those who had unconsciously rowed him to the island. The other he recognized with a start as the possessor of the face which had peered through the transom on the memorable night in Hampton, when plans for the experiments on the island were in process of being formulated. In other words, the third member of the party was none other than Nordstrom Berghoff, the spy.

Instantly many things that had been vague to Rob crystallized into a clear understanding of the situation. The signals from the island, the indignation of Barton over the presence of the Boy Scouts, and the stealing of the plans and models, all stood out plainly now as being part of an elaborate plot of which Berghoff was the mainspring.

A wave of indignation swept over the boy as he contemplated the rascals within the hut gloating over the things they had obtained from the treacherous Barton.

"The scoundrels," he thought; "so they think they can rob Uncle Sam of one of the greatest submarines ever invented, and do so with impunity! I don't care what happens, I'll fool them if I can."

With this resolve firmly embedded in his mind, Rob crept closer to the window. By skillful maneuvering he was at last almost under the casement. In this position every word uttered within the hut was clear to him.

He heard Berghoff chuckling gleefully over the manner in which the night's work had been carried out.

"Undt not a vun of dose Boy Scouts knew anting aboudt idt," he exclaimed.

"No," rejoined one of his companions, a swarthy man with a pallid face on which there stood out a bristly beard; "those kids were out of the game so far as we were concerned. That Barton is a slick one, all right."

"Well, he's getting well paid for the job," struck in the third man, who was short and stocky, with a crop of rough, reddish hair and a protruding chin that gave him a "bull doggy" aspect.

"Of course, he gedts vell paid," rejoined Berghoff; "dis job is vorth de naval supremacy of the worldt to der country vot I represent."

"As if we didn't know that as well as you," rejoined the red-haired man. "It was lucky we worked in the same machine shop in Bridgeport with Barton and knew he was a man who could be bought."

"Yes, there isn't much that he wouldn't do for money," chimed in the pallid-faced man.

"Vell, ledt us see if dese plans are all righdt, or if ve must get some more of dem," remarked Berghoff.

From his manner of examining the intricate prints and plans, Rob knew that the man, as were most probably his two companions, was an engineer of no mean ability. With a small pocket scale he went over every scrap of paper and then fell to examining the models. From his expression, Rob judged that Barton had served the rascal well. Berghoff declared the plans and the models all that would be required to produce a Peacemaker almost the exact duplicate of Mr. Barr's diving-boat.

"Well, when do we make our getaway?" queried the red-haired man when the examination was concluded.

"To-morrow ve go," declared Berghoff. "In New York I catch der steamer for Europe undt you two scatter verefer you like."

Rob felt his face flush with indignation, and at the same time he experienced a sort of hopeless feeling of indecision. The plans and the models lay there, almost within his reach, but so far as the possibility of recovering them was concerned, they might as well have been in China.

"If only all the boys were here," he thought, "it would be possible to 'rush' those scoundrels and secure all their loot."

Finally Rob came to the decision to remain where he was for the present and see if some opportunity would not present itself to recover the articles of such vital importance to Uncle Sam's Government.

The men talked on, conversing in low tones, and presently the red-headed man started to prepare some food on an oil stove, which must have been brought from the motor boat earlier in the day. Till sundry appetizing odors began to drift out to him from the plotter's cookery, Rob did not realize that he was hungry. Before long, however, his desire for food became almost overwhelming. It was tantalizing to lie out there in the dark, tired and hungry, and hear within the hut the clatter of knives and forks and inhale the odors of what was evidently a hearty meal.

At length the men stopped eating, and Rob heard them discussing whether they should sleep in the hut or on board their motor boat. The boy pricked up his ears as he listened. If only they decided to sleep on the boat and leave the models and plans in the hut, he would have a chance to recover the stolen property and make away with it in the beached rowboat before dawn.

Rob could hardly restrain an exclamation of delight when the men came to the decision to pass the night on their boat.

"What are you going to do with this stuff?" inquired the pallid-faced man with the stubbly beard, indicating the mass of papers and models.

"Oh, we'll leave that here till morning," was Berghoff's response; "dere is no use in taking idt by der boat now."

"Goodness," thought Rob, "I sure am in luck! It will be no trick at all to get that stuff as soon as they have gone, and carry it back to the island. I almost wish it was going to be a harder task. It's a bit too much like burglary to suit me."

But Rob was not to have such an easy time of it as he anticipated.