CHAPTER XXII.

  A MIDNIGHT ADVENTURE.

  Half an hour after her start, the _Viper_ glided alongside the islandfrom which Merritt had seen the signals go up the afternoon before. Hecould not forbear to take a glance at Barton as the ensign ordered theengines stopped.

  The machinist was stooping over the motor to hide his agitation; but bythe trembling of his hands Merritt could tell that the fellow wasapprehensive of something that might involve himself. As soon as theanchor dropped, the motor boat's dinghy was drawn up alongside and theensign and Merritt boarded it. The others were left on board the _Viper_with whispered orders from the officer to watch Barton's every move.The island was a small one, and from its highest point it was possibleto see all around it. To Merritt's bitter disappointment, however, nosign of another motor boat was in sight. Their quarry had flown.

  "There's but one thing to do," declared the ensign; "we must make forthat small hut over yonder and search it thoroughly. It may yield a clueof some kind."

  A short walk brought them to the hut which had been the scene of thestirring events of the preceding night. Hardly had they entered the doorbefore Merritt gave a start of surprise and a swift exclamation.

  "Look! Look there!" he cried. "There's Rob's hat!"

  Sure enough, lying in a corner was the boy leader's campaign hat, whichhe had lost in the scuffle with Mike and Gyp.

  "Well, that shows conclusively enough that he was here last night, andfrom that upset table and the general look of things, I should imaginethere had been a pretty lively scrap here," commented the ensign.

  "But where can Rob be now?"

  "Probably fearing discovery if they remained here, the men who havetaken the plans and the models carried him off, too."

  "How will it ever be possible to obtain a clew as to where they havegone?"

  The ensign's answer appeared enigmatical.

  "Could you describe the motor boat you saw off here yesterday?"

  "Well, she was of a very remarkable color--a light green, with a signalmast sticking up amidships. Then, too, her cabin was unusually high."

  "Good. Such a boat as that ought not to be very hard to locate."

  "I don't quite understand."

  "Well, then I'll explain. These waters are fairly well traveled, and byworking our wireless we may be able to get into communication with someboat similarly equipped, which may have seen that green motor boat."

  "Cracky, that's a good idea," cried the admiring boy; "let's go back andtry it at once."

  "Yes, it's small use our waiting about here. The rascals overreached usby getting away as quick as possible. I suppose they didn't want to runany chances of discovery."

  The return to the _Viper_ was quickly made, and the motor boat wasdriven back to the Submarine Island at top speed. Barton tried with allhis might to overhear what was said in the bow of the boat where the BoyScouts had gathered; but the ensign was careful to keep his voice low,and then, too, the noise of the engines precluded the machinist fromcatching a word, hard as he strained his ears.

  Under the tutoring of Hiram Nelson, the wireless scout, the others hadall become fair operators. It was agreed that day and night one of themshould be at the apparatus, seeking for news of the green motor boat.

  It was the ensign's opinion that the craft would not put into a portimmediately, fearing a hue and cry, but would cruise about or hide insome little frequented part of the coast. But he hoped that if thewireless "caught" some vessel that had spoken to her, he could at leastobtain a line on which direction she had taken.

  The first "session" at the wireless was taken by Hiram, then came theothers in rotation; but when at ten o'clock that night Donald, who hadlearned wireless on his father's yacht, came on duty, there had come noword from the air of a green motor boat. Several ships had been spokento, but not one reported anything to give the boys hope.

  "Well, good-night, old man," said Merritt, as Donald, who relieved him,came on duty, "and good luck."

  "I'll keep a good watch out, all right," was the earnest response."It's our only way to get poor old Rob back."

  "I'm afraid so," sighed Merritt, leaving the place with a despondentair. As Donald had said, it was a chance--but what a long, seeminglyhopeless one!

  Donald, left alone, began sending out calls, and every little while hepaused for an answer out of space to his appeals. As he pressed thesending key the blue, lithe spark leaped and crackled between its pointslike a fiery snake. Then all would become silent again as he listenedfor an answer to his call.

  Once he caught a steamer bound north and carried on quite a conversationwith its operator. He felt quite lonesome when he closed down hissending apparatus with a parting "good-bye."

  It was very still about the encampment. So still, in fact, that the boybegan to feel more and more lonesome. He longed for someone to talk to;but he knew that chance would not come till Tubby, his relief,appeared.

  The stout youth was almost due when Donald suddenly got intocommunication with a steamer called the _Cambria_, bound north from NewOrleans to New York. He put his customary query about the green motorboat.

  "A green motor boat?" came back the reply.

  "Yes," flashed Donald.

  "With one signal mast and a high cabin?"

  "Yes! yes," shot out Donald, pounding the key excitedly. "Have you seensuch a craft?"

  "We sighted her this evening."

  The boy's fingers shook as he wrote down the reply with flying pencil onthe scratch pad at his elbow.

  "Down off some islands about Lat. 80 deg., Long. 33 deg.," came theanswer. "She was coming straight toward us and then all of a sudden sheheaded away. Seemed like she didn't want to get near us. Is that all?"

  "Yes; good-bye, and thank you," flashed back Donald exultantly.

  His fingers had hardly left the key before he was startled by a softfootfall behind him.

  The boy wheeled like a flash and then almost fell off his chair. Facinghim, with an ugly-looking revolver in his hand, was Barton, themachinist.

  There was a mean sneer on his sinister face as he snarled out:

  "Let me see that message and let me see it quick."

  "I've got no message for you," responded Donald, determined not to letthe man know that he had information of the green motor boat'swhereabouts.

  "That's a lie," snarled Barton; "don't monkey with me. I've got this gunand, jingo, I know how to use it, too."