“I’ll never promise anything like that,” exclaimed Mart, recoiling with horror.

“You will, or else—” The old balloonist paused.

“Or else what?”

“I will keep you here, and starve you into submission.”

CHAPTER XXXIII.—LEO TO THE RESCUE.

Leo’s first care, after leaving the hospital, was to ask about Mart.

He was astonished to learn at the hotel at which the party was stopping that nothing had been seen of the lad since the balloon had left the exhibition grounds.

Greson had gone for the balloon late the day before.

“Found the balloon all right, but didn’t see a single trace of the boy,” said the assistant.

“That is queer,” mused Leo. “Can it be that he tumbled down in some out-of-the-way place and was killed?”