“What had we better do to him?” asked Andy, as they neared the prostrate man.

“Tie him up so he can’t get away again,” replied Frank, as he glanced at the seaman who was rapidly rowing away. “If we keep him, now that we’ve got him, he may tell us what we want to know. And we’ve got the wreck of the motor boat, too. We sure ought to get at the bottom of this mystery now.”

“Well, we deserve something after all we went through,” remarked the younger lad, as he thought of the rising tide in the cave.

“That fellow is in a hurry all right,” went on Frank, with a wave of his hand toward the sailor who was now some distance out. “I guess he hit him a pretty hard blow.”

“Maybe he killed that man, and is afraid we’ll arrest him,” suggested Andy.

“Nonsense! I don’t believe that man is dead.”

They were close to him now and stopped to observe the quiet figure. They hesitated for a moment, for, though they had made up their minds to make the man a prisoner, it was the first time they had done anything of the sort, and, naturally, they were a little timid.

Suddenly the figure on the sands stirred, and there came a murmur from the mysterious man.

“If we’re going to do anything, we’d better get at it,” suggested Andy. “He’ll come to his senses in a minute and we’ll have our hands full. He’s a powerful fellow.”

“That’s so. I wonder where there’s some rope?” asked Frank.

Andy motioned to the wreck of the motor boat, near which the man lay.

“There’s plenty,” he said. “They had a long rope to tow it with. I’ll get some.”

Holding the cord in readiness, the two brothers approached the man, one on either side.

“You take his feet, and I’ll attend to his hands,” whispered Frank. “Have a slip-noose ready to put on, and pull it tight. Then take several turns and we’ll truss him up.”

They worked silently and rapidly. Andy slipped the coil of rope about the man’s ankles, and pulled the noose taut. As he was doing this the man stirred and murmured:

“I’ll get even with you for this, Hank Splane!”

“Quick! He’ll come to in a minute!” whispered Andy.

“I’ve got him,” answered Frank. As one of the man’s arms was partly under him the lad had to pull it out before he could slip the noose around it. But he finally accomplished this, and, just as he had it tight, the fellow suddenly sat up.

“Here! What’s this? Splane, are you crazy to tie me up this way? Let me go, I say, or I’ll make you sorry for this. Let me go, I say!”

He was struggling violently, swaying to and fro as he sat on the sands. Then his vision, which was probably ............