Another half-hour and we reached the end of the lane by which we had first entered the cavern.  We stood gazing at it with eyes of desire, but we knew how little chance there was of the thing being unguarded at the farther end.  We knew then, of course, and only too well, why the Incas had not followed us into the cavern.

“Perhaps they are gone,” said Harry.  “They can’t stay there forever.  I’m going to find out.”

He sprang on the edge of a boulder at the mouth of the passage and disappeared on the other side.  In fifteen minutes he returned, and I saw by the expression on his face that there was no chance of escape in that direction.

“They’re at the other end,” he said gloomily; “a dozen of ’em.  I looked from behind a rock; they didn’t see me.  But we could never get through.”

We turned then, and proceeded to the third wall and followed it.  But we really had no hope of finding an exit since Harry had said that he had previously explored it.  We were possessed, I know, by the same thought:  should we venture to follow the fourth wall?  Alone, none of us would have dared; but the presence of the others lessened the fear of each.

Finally we reached it.  The corner was a sharp right angle, and there were rifts and crevices in the rock.

“This is limestone,” I said, “and if we find an exit anywhere it will be here.”

I turned to the right and proceeded slowly along the wall, feeling its surface with my hand.

We had advanced in this manner several hundred yards when Desiree suddenly sprang forward to my side.

“See!” she cried, pointing ahead with her spear.

I followed the direction with my eye, and saw what appeared to be a sharp break in the wall.

It was some fifty feet away.  We reached it in another moment, and I think none of us would have been able to express the immeasurable relief we felt when we saw before us a broad and clear passage leading directly away from the cavern.  It was very dark, but we entered it almost at a run.

I think we had not known the extent of our fear of that thing in the cavern until we found the means of escape from it.

We had gone about a hundred feet when we came to a turn to the left.  Harry stumbled against the corner, and we halted for an instant to wait for him.

Then we made the turn, side by side—­and then we came to a sudden and abrupt stop, and a simultaneous gasp of terror burst from our lips.

Not three feet in front of us, blocking the passage completely, stood the thing we thought we had escaped!

The terrible, fiery eyes rolled from side to side as they stared straight into our own.

Chapter XVIII.

A victory and A conversation.

We stood for a long moment rooted to the spot, unable to move.  Then, calling to Harry and grasping Desiree by the arm, I started to turn.