that small hut over yonder and search it thoroughly. It may yield a clue
of some kind."

A short walk brought them to the hut which had been the scene of the
stirring events of the preceding night. Hardly had they entered the door
before 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, which
he had lost in the scuffle with Mike and Gyp.

"Well, that shows conclusively enough that he was here last night, and
from that upset table and the general look of things, I should imagine
there 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 have
taken the plans and the models carried him off, too."

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

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 signal
mast 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 by
working our wireless we may be able to get into communication with some
boat similarly equipped, which may have seen that green motor boat."

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

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

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

Under the tutoring of Hiram Nelson, the wireless scout, the others had
all become fair operators. It was agreed that day and night one of them
should 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 port
immediately, fearing a hue a