Jimmie knew, from the flounderings on the floor, that the fellow was again trying to get rid of the rope. He stepped to the door and lifted a hand in warning, then slid the bolts and guards so the water chamber door would open from the outside, then stepped back into the larger apartment and closed the door.
He heard a rush of water and knew that some one was entering. Then, satisfied that all was well, he turned to his prisoner.
The fellow was half out of the rope, and one hand was sneaking toward a heavy ax which lay not far off.
"Cut that!" cried the boy.
He stood guarding the man while the water chamber filled and emptied. Then the door opened and Ned came in, helmet in hand. First, he turned a screw and the trouble at the air machine ceased.
"What the dickens!"
Ned stopped short in the middle of the room as he turned and gazed in amazement at the prisoner.
"I've been fishin'," Jimmie explained, with a chuckle.
"What is it you caught?" asked Ned.
"This," said Jimmie, "is the original sea serpent!"