"Got a new job for you to-day, Chunky," announced Ned Rector while
cinching the pack girths.

"What is it?"

"We've decided to let you follow along behind with a sharp stick and
prod the mules so they will make better time."

"Think I'll wait till after twelve o'clock to-night," answered the fat
boy.

They were off soon after that, but the mules had never seemed to move
as slowly as they did that morning. Instead of an hour, more than two
hours had passed before they finally came within hailing distance of
the camp-fire. For some time, they had been finding difficulty in
keeping it in sight, as the fire appeared to be dying down.

Tad shouted to attract the attention of the campers or the Professor
to let them know the Pony Riders were coming. There was no reply,
which caused the lads to wonder.

So they pushed the mules all they could, a vague apprehension that all
was not as it should be, growing in their minds. They soon came upon
the object of their search. What they found was a smouldering
camp-fire.

"The camp is deserted," groaned Tad.

Not a person save themselves was within sight or sound. Professor
Zepplin, too, had disappeared.