Five o’clock had come and gone.  The sun was partly bidden by the ridge of the Guadalupes towards which the Pony Rider Boys were slowly drawing.  Ned called up to the professor who was riding at the head.

“Where are we going to make camp, Professor?”

“Tad will decide that,” answered Professor Zepplin without looking back.

“Near a stream, of course,” answered Butler.

“Any mosquitoes there?” demanded Stacy.

“No odds, if there are,” retorted Ned.  “They wouldn’t bite you.”

“Not if they had got at you first,” returned Stacy solemnly.  “There’s a level place in there by the creek.”

“I see it.  I’ll ride on and have a closer look at it.”

Butler spurred his pony ahead of the others.  Reaching the foothills of the range he shaded his eyes, gazing up into the cool, green valley or canyon that led into the mountains.

“I guess this will do very well, boys,” he said.  “I—–­”

Bang!

“Wow!”

Stacy with a howl of terror slid from his pony, sending up a little cloud of dust as he collapsed on the plain.

“Wha---what---what-----” gasped the professor.

Bang!

Professor Zepplin’s sombrero was snipped from his head.  Stacy lay groaning on the ground.

“Ride for the rocks!” shouted Tad as shot after shot began popping from somewhere in the mountains, the bullets screaming over their heads close to their ears or snipping up flecks of dust in the plain.

Tad drove his pony straight at Stacy Brown.  He scooped the fat boy up by the collar and rode madly for the protection of the rocks, Chunky’s heels dragging on the ground.  The others rode madly after them, while the shots were still being fired at them.  It was an exciting moment.  No one knew what the shooting meant, nor did they know whether Stacy really had been hit or not.  There was no time to stop to reason the matter out.  It was a case of getting to cover as fast as horse-flesh would carry them.

CHAPTER II

A MYSTERIOUS ATTACK

“Pull in close!” cried Tad.

“Where is it coming from?” shouted Ned.

“I don’t know.  I haven’t had time to look.  Look out there!”

Professor Zepplin, somewhat slower than the others, had halted a little distance out from the foothills.  A bullet threw up a little cloud of dust just to one side of where he was sitting on his pony, followed by a report somewhere up in the mountains.

“Stop that!  Stop it, I tell you!” bellowed the professor, waving his sombrero.  Almost ere the words were out of his mouth, the sombrero was shot from his hand and went spinning out to the rear.  Professor Zepplin did not wait for further parley.  He turned his horse, dashing for the protection of the foothills.

In the meantime, Tad Butler had leaped from his pony, placing Stacy on the ground.  It was observed that there was blood on the fat boy’s left cheek, but his eyes, wide and frightened, were staring up at the boys now gathering about him.