either
side of the pair. Four weapons covered the group in the outer room.

The three men, who had advanced well to the center of the room, stared
dumbfounded at these apparitions. Then amazement gave place to anger,
and one of the trio made a move as if to draw his revolver.

"None of that," commanded Jack, sternly. "Up with them quick or I'll
shoot."

Three pairs of hands were unwillingly elevated. Two of the men wore
sheepskin jackets and leather helmets and the boys surmised correctly
that they had been up in the airplane. Bob felt certain they were
Morales and Von Arnheim, the two who had made the trip to the East to
steal Mr. Hampton's papers and whom he had foiled in that purpose, but
who had succeeded in stealing the airplane and making their way to
Mexico in it. The other was a rangy man of about twenty-six, keen and
shrewd-looking, and had the appearance of an American. Evidently he
was the guardian of the cave. And it was he who had moved to draw his
weapon when surprised. A tough customer and one to be watched, thought
the boys.

"Face about," ordered Jack.

They obeyed.

"Keep them covered, Tom," Jack then commanded. "Well search them."

With weapons held ready, the three boys advanced. At that moment, the
caretaker of the cave took one step forward and instantly the lights
in both rooms faded out and the cave was in inky darkness.

He had pressed a button in the floor, switching off the lights.

The boys were so taken by surprise that for a moment they did not
fire. Neither did Tom, for fear of hitting them as they were in front
of him. This gave their three enemies an opportunity to shift position
and fling themselves prone.

When after their surprise, the boys did fire, their bullets merely
pinged against the distant wall and did no damage. But the flash of
their weapons betrayed their positions and answering bullets came
uncomfortably close. One swept Jack's hat from his head.

From behind them Tom Bodine's revolver spoke, as the enemy thus
betrayed themselves. The soft thud of a bullet striking flesh, a
groan, choked off in the middle, a hasty scrambling to get away from
the danger point on the part of the man struck, then silence.

This silence was so profound the boys seemed to hear the beating of
their own hearts, and tried to hold their breath for fear of betrayal.
They had thrown themselves prone after the first volley and lay so
close they were touching, Jack in the middle.

Eac