“Good,” exclaimed Rob, “that’s something and half confirms my suspicion.  Go on, Andy, what else?”

“Well, we examined the marks carefully and found that two pairs of feet wore good shoes and the third a very broken, disreputable pair.”

“Yes,” exclaimed Rob, while the others listened breathlessly.

“Of course that indicated to us that three persons must have carried Joe off—­for I don’t think there’s much doubt now that he was carried off, do you?”

“I don’t,” said Rob sadly, “but for what possible motive?”

“I have it,” suddenly exclaimed Tubby Hopkins, snapping his fingers, “you remember the day of the aeroplane model contest?”

“Yes, but what—­” began Rob.

“Has that to do with it,” finished Tubby for him.  “Everything.  It was Joe who first told the committee that Jack’s model was a bought one and so lost him the fifty-dollar prize.”

“By cracky, that’s right!” assented Rob, “and you think that Jack and his gang have carried him off in revenge for it?”

“Looks that way to me,” nodded the stout youth.

“Why, they wouldn’t dare,” began Andy Bowles.

“Oh, yes, they would,” amended Rob bitterly, “they’d dare anything to get even on us for their fancied wrongs.  But whose could have been the broken ragged shoes?” he asked, suddenly taking up another train of thought.

“Hank Handcrafts, the beach-comber’s,” suggested Tubby.

“Gee Whillikens!  I’ll bet a cracker that’s the solution,” cried Andy, “and now I come to think of it I heard, before we left, that Jack and his gang had gone camping.”

“Where?”

“Up around the Upper Inlet somewhere.  You know that’s full of islands and as there’s no drinking water there few people ever think of frequenting the place.  If they wanted to do anything like carrying off Joe that is where they would have been likely to go.”

“You may be right, Andy.  It’s worth looking into, anyway,” declared Rob.  “I’ll leave a note here for the others and we’ll take a run over there in the Flying Fish.  If Joe is there we’ll get him out.”

“And in jig time, too,” chimed in Ernest Thompson.

“Come on, boys, get some gasoline, hop in the dinghy and let’s get aboard.  We’ve got to move fast if we’re to accomplish anything.  You get the boat, Andy, while I write a line to tell the others what we’ve gone after.”

The young leader hastily ran into his tent and sitting down at the table dashed off these lines: 

“Boys, we think we have a clue to Joe’s whereabouts.  Have gone after him.  Keep camp in regular way while we are gone.  Hiram Nelson is leader, and Paul Perkins corporal, in our absence.

“Rob Blake, Leader,

“Eagle Patrol, B. S. of A.”

With a piece of chalk the boy marked a rough square and an arrow on a tree—­the arrow pointing to a spot in the sand in which he buried the letter.