“I guess you wrenched your nerve,” sneered Eph.

Then, headed by Masterson, with the pistol in his grasp, they began to ascend the pathway.  Dick was in a quandary.  But he decided that the only way to tackle the problem was to take the bull by the horns.  As Masterson reached the mouth of the cave the boy dashed out like a redheaded thunderbolt.

Taken utterly by surprise, Masterson stepped back.

Bang!

The pistol went off in the air and the next instant Masterson, despite his efforts to save himself, toppled off the narrow path and went rolling down the bank into the river.  Luckily for him, he was a good swimmer, and struck out lustily as he came to the surface.

“Wow!” yelled Dick, and charged like a young buffalo at Eph.

Young Compton tried to strike him but Dick, with lowered head, charged him in the stomach.  With a grunt Eph fell back, and in his fall knocked over Sam Higgins, just behind him.

“Whoop-ee!” shouted Dick, rejoicing in his triumph.  He leaped over the recumbent forms of Eph and Sam and dashed down the path to the place where he had beached his boat.

He jumped on board and poled off just as young Masterson reached the shore and pulled himself out of the water.

“You infernal young spy!” shrieked Masterson, beside himself with rage, “I’ll get even with you for this, see if I don’t!”

Sam and Eph, who had picked themselves up, shouted other threats at Dick.  But he turned round and, with a pleasant smile, waved a hand as the current carried his boat round the bend.  He felt in high good humor at the way he had gotten out of a difficult situation.  It was fortunate for him, though, that he had taken Masterson and his cronies so utterly by surprise, otherwise the adventure might have had a different conclusion.

He had established one fact, however, and that was that Masterson and the others were spying on them every night and watching every step in their preparations for the departure for Rattlesnake Island.

That night a strict watch was kept in the camp, all the adventurers taking turns at sentry duty.  But nobody came near the place.

CHAPTER XXVII.

THE PROFESSOR’S SECOND DILEMMA.

Early the next day old man McGee paid them a call.  He came to take back the burro they had hired from him for convenience in getting back and forth from Yuma.  He also wanted to get a ladder which had been left at the deserted shanty.  The old man rode into camp on a razor-backed horse and professed great astonishment when he saw how nearly completed the work on the Wondership was.

“But you kain’t fool me,” he said knowingly.  “I may be old but I’m wise.  That thing fly?  Why, you might as well tell me the Nat’nul Hotel in Yuma could go kerflopping about in the air.  By the way,” he went on, “frum ther talk in ther town you ain’t ther only ones as is goin’ down ther river.  There’s three young chaps has bought two boats and allows that they’re fixin’ to take a trip.”