Not a hundred feet to the rear we saw a group of Incas rushing along the passage toward us.  Harry wheeled about, raising his spear, but I grasped him by the arm, crying, “Run; it’s our only chance!” The next moment we were leaping forward side by side down the passage.

It would have fared ill with any who appeared to block our way in that mad dash; but it remained clear.  The corridor led straight ahead, with never a turn.  We were running as we had never run before; the black walls flashed past us an indistinguishable blur, and the open doorways were blended into one.

Glancing back over my shoulder, I saw that the small group of Incas was no longer small.  Away to the rear the corridor was filled with rushing black forms.  But I saw plainly that we were gaining on them; the distance that separated us was twice as great as when we had first started to run.

“How about it?” I panted.  “Can you hold out?”

“If it weren’t for this knee,” Harry returned between breaths and through clenched teeth.  “But—­I’m with you.”  He was limping painfully, and I slackened my pace a little, but he urged me forward with an oath, and himself sprang to the front.  His knee must have been causing him the keenest agony; his face was white as death.

Then I uttered a cry of joy as I saw a bend in the passage ahead.  We reached it, and wheeled to the right.  There was solid wall on either side; the series of doors was ended.

“We’ll shake ’em off now,” I panted.

Harry nodded.

A short distance ahead we came to another cross-passage, and turned to the left.  Glancing over my shoulder, I saw that our pursuers had not yet reached the first turn.  Harry kept in the lead, and was giving me all I could do to keep up with him.

We found ourselves now in a veritable maze of lanes and cross-passages, and we turned to one side or the other at every opportunity.  At length I grasped Harry by the arm and stopped him.  We stood for two full minutes listening intently.  There was absolutely no sound of any kind.

“Thank Heaven!” Harry breathed, and would have fallen to the ground if I had not supported him.

We started out then in search of water, moving slowly and cautiously.  But we found none, and soon Harry declared that he could go no further.  We sat down with our backs against the wall of the passage, still breathing heavily and all but exhausted.

In that darkness and silence the minutes passed into hours.  We talked but little, and then only in whispers.  Finally Harry fell into a restless sleep, if it may be called that, and several times I dozed off and was awakened by my head nodding against the stone wall.

At length, finding Harry awake, I urged him to his feet.  His knee barely supported his weight, but he gritted his teeth and told me to lead on.

“We can wait—­” I began; but he broke in savagely: