As we advanced up the river which winds beneath the Golden Cliffs out of the bowels of the Mountains of Otz to mingle its dark waters with the grim and mysterious Iss the faint glow which had appeared before us grew gradually into an all-enveloping radiance.

The river widened until it presented the aspect of a large lake whose vaulted dome, lighted by glowing phosphorescent rock, was splashed with the vivid rays of the diamond, the sapphire, the ruby, and the countless, nameless jewels of Barsoom which lay incrusted in the virgin gold which forms the major portion of these magnificent cliffs.

Beyond the lighted chamber of the lake was darkness—what lay behind the darkness I could not even guess.

To have followed the thern boat across the gleaming water would have been to invite instant detection, and so, though I was loath to permit Thurid to pass even for an instant beyond my sight, I was forced to wait in the shadows until the other boat had passed from my sight at the far extremity of the lake.

Then I paddled out upon the brilliant surface in the direction they had taken.

When, after what seemed an eternity, I reached the shadows at the upper end of the lake I found that the river issued from a low aperture, to pass beneath which it was necessary that I compel Woola to lie flat in the boat, and I, myself, must need bend double before the low roof cleared my head.

Immediately the roof rose again upon the other side, but no longer was the way brilliantly lighted. Instead only a feeble glow emanated from small and scattered patches of phosphorescent rock in wall and roof.

Directly before me the river ran into this smaller chamber through three separate arched openings.

Thurid and the therns were nowhere to be seen—into which of the dark holes had they disappeared? There was no means by which I might know, and so I chose the center opening as being as likely to lead me in the right direction as another.

Here the way was through utter darkness. The stream was narrow—so narrow that in the blackness I was constantly bumping first one rock wall and then another as the river wound hither and thither along its flinty bed.

Far ahead I presently heard a deep and sullen roar which increased in volume as I advanced, and then broke upon my ears with all the intensity of its mad fury as I swung round a sharp curve into a dimly lighted stretch of water.

Directly before me the river thundered down from above in a mighty waterfall that filled the narrow gorge from side to side, rising far above me several hundred feet—as magnificent a spectacle as I ever had seen.

But the roar—the awful, deafening roar of those tumbling waters penned in the rocky, subterranean vault! Had the fall not entirely blocked my further passage and shown me that I had followed the wrong course I believe that I should have fled anyway before the maddening tumult.

Thurid and the therns could not have come this way. By stumbling upon the wrong course I had lost the trail, and they had gained so much ahead of me that now I might not be able to find them before it was too late, if, in fact, I could find them at all.

It had taken several hours to force my way up to the falls against the strong current, and other hours would be required for the descent, although the pace would be much swifter.

With a sigh I turned the prow of my craft down stream, and with mighty strokes hastened with reckless speed through the dark and tortuous channel until once again I came to the chamber into which flowed the three branches of the river.

Two unexplored channels still remained from which to choose; nor was there any means by which I could judge which was the more likely to lead me to the plotters.

Never in my life, that I can recall, have I suffered such an agony of indecision. So much depended upon a correct choice; so much depended upon haste.

The hours that I had already lost might seal the fate of the incomparable Dejah Thoris were she not already dead—to sacrifice other hours, and maybe days in a fruitless exploration of another blind lead would unquestionably prove fatal.

Several times I essayed the right-hand entrance only to turn back as though warned by some strange intuitive sense that this was not the way. At last, convinced by the oft-recurring phenomenon, I cast my all upon the left-hand archway; yet it was with a lingering doubt that I turned a parting look at the sullen waters which rolled, dark and forbidding, from beneath the grim, low archway on the right.

And as I looked there came bobbing out upon the current from the Stygian darkness of the interior the shell of one of the great, succulent fruits of the sorapus tree.

I could scarce restrain a shout of elation as this silent, insensate messenger floated past me, on toward the Iss and Korus, for it told me that journeying Martians were above me on that very stream.

They had eaten of this marvelous fruit which nature concentrates within the hard shell of the sorapus nut, and having eaten had cast the husk overboard. It could have come from no others than the party I sought.

Quickly I abandoned all thought of the left-hand passage, and a moment later had turned into the right. The stream soon widened, and recurring areas of phosphorescent rock lighted my way.

I made good time, but was convinced that I was nearly a day behind those I was tracking. Neither Woola nor I had eaten since the previous day, but in so far as he was concerned it mattered but little, since practically all the animals of the dead sea bottoms of Mars are able to go for incredible periods without nourishment.

Nor did I suffer. The water of the river was sweet and cold, for it was unpolluted by decaying bodies—like the Iss—and as for food, why the mere thought that I was nearing my beloved princess raised me above every material want.

As I proceeded, the river became narrower and the current swift and turbulent—so swift in fact that it was with difficulty that I forced my craft upward at all. I could not have been making to exceed a hundred yards an hour when, at a bend, I was confronted by a series of rapids through which the river foamed and boiled at a terrific rate.

My heart sank within me. The sorapus nutshell had proved a false prophet, and, after all, my intuition had been correct—it was the left-hand channel that I should have followed.

Had I been a woman I should have wept. At my right was a great, slow-moving eddy that circled far beneath the cliff's overhanging side, and to rest my tired muscles before turning back I let my boat drift into its embrace.

I was almost prostrated by disappointment. It would mean another half-day's loss of time to retrace my way and take the only passage that yet remained unexplored. What hellish fate had led me to select from three possible avenues the two that were wrong?

As the lazy current of the eddy carried me slowly about the periphery of the watery circle my boat twice touched the rocky side of the river in the dark recess beneath the cliff. A third time it struck, gently as it had before, but the contact resulted in a different sound—the sound of wood scraping upon wood.

In an instant I was on the alert, for there could be no wood within that buried river that had not been man brought. Almost coincidentally with my first apprehension of the noise, my hand shot out across the boat's side, and a second later I felt my fingers gripping the gunwale of another craft.

As though turned to stone I sat in tense and rigid silence, straining my eyes into the utter darkness before me in an effort to discover if the boat were occupied.

It was entirely possible that there might be men on board it who were still ignorant of my presence, for the boat was scraping gently against the rocks upon one side, so that the gentle touch of my boat upon the other easily could have gone unnoticed.

Peer as I would I could not penetrate the darkness, and then I listened intently for the sound of breathing near me; but except for the noise of the rapids, the soft scraping of the boats, and the lapping of the water at their sides I could distinguish no sound. As usual, I thought rapidly.

A rope lay coiled in the bottom of my own craft. Very softly I gathered it up, and making one end fast to the bronze ring in the prow I stepped gingerly into the boat beside me. In one hand I grasped the rope, in the other my keen long-sword.

For a full minute, perhaps, I stood motionless after entering the strange craft. It had rocked a trifle beneath my weight, but it had been the scraping of its side against the side of my own boat that had seemed most likely to alarm its occupants, if there were any.

But there was no answering sound, and a moment later I had felt from stem to stern and found the boat deserted.

Groping with my hands along the face of the rocks to which the craft was moored, I discovered a narrow ledge which I knew must be the avenue taken by those who had come before me. That they could be none other than Thurid and his party I was convinced by the size and build of the boat I had found.

Calling to Woola to follow me I stepped out upon the ledge. The great, savage brute, agile as a cat, crept after me.

As he passed through the boat that had been occupied by Thurid and the therns he emitted a single low growl, and when he came beside me upon the ledge and my hand rested upon his neck I felt his short mane bristling with anger. I think he sensed telepathically the recent presence of an enemy, for I had made no effort to impart to him the nature of our quest or the status of those we tracked.

This omission I now made haste to correct, and, after the manner of green Martians with their beasts, I let him know partially by the weird and uncanny telepathy of Barsoom and partly by word of mouth that we were upon the trail of those who had recently occupied the boat through which we had just passed.

A soft purr, like that of a great cat, indicated that Woola understood, and then, with a word to him to follow, I turned to the right along the ledge, but scarcely had I done so than I felt his mighty fangs tugging at my leathern harness.

As I turned to discover the cause of his act he continued to pull me steadily in the opposite direction, nor would he desist until I had turned about and indicated that I would follow him voluntarily.

Never had I known him to be in error in a matter of tracking, so it was with a feeling of entire security that I moved cautiously in the huge beast's wake. Through Cimmerian darkness he moved along the narrow ledge beside the boiling rapids.

As we advanced, the way led from beneath the overhanging cliffs out into a dim light, and then it was that I saw that the trail had been cut from the living rock, and that it ran up along the river's side beyond the rapids.

For hours we followed the dark and gloomy river farther and farther into the bowels of Mars. From the direction and distance I knew that we must be well beneath the Valley Dor, and possibly beneath the Sea of Omean as well—it could not be much farther now to the Temple of the Sun.

Even as my mind framed the thought, Woola halted suddenly before a narrow, arched doorway in the cliff by the trail's side. Quickly he crouched back away from the entrance, at the same time turning his eyes toward me.

Words could not have more plainly told me that danger of some sort lay near by, and so I pressed quietly forward to his side, and passing him looked into the aperture at our right.

Before me was a fair-sized chamber that, from its appointments, I knew must have at one time been a guardroom. There were racks for weapons, and slightly raised platforms for the sleeping silks and furs of the warriors, but now its only occupants were two of the therns who had been of the party with Thurid and Matai Shang.

The men were in earnest conversation, and from their tones it was apparent that they were entirely unaware that they had listeners.

"I tell you," one of them was saying, "I do not trust the black one. There was no necessity for leaving us here to guard the way. Against what, pray, should we guard this long-forgotten, abysmal path? It was but a ruse to divide our numbers.

"He will have Matai Shang leave others elsewhere on some pretext or other, and then at last he will fall upon us with his confederates and slay us all."

"I believe you, Lakor," replied the other, "there can never be aught else than deadly hatred between thern and First Born. And what think you of the ridiculous matter of the light? 'Let the light shine with the intensity of three radium units for fifty tals, and for one xat let it shine with the intensity of one radium unit, and then for twenty-five tals with nine units.' Those were his very words, and to think that wise old Matai Shang should listen to such foolishness."

"Indeed, it is silly," replied Lakor. "It will open nothing other than the way to a quick death for us all. He had to make some answer when Matai Shang asked him flatly what he should do when he came to the Temple of the Sun, and so he made his answer quickly from his imagination—I would wager a hekkador's diadem that he could not now repeat it himself."

"Let us not remain here longer, Lakor," spoke the other thern. "Perchance if we hasten after them we may come in time to rescue Matai Shang, and wreak our own vengeance upon the black dator. What say you?"

"Never in a long life," answered Lakor, "have I disobeyed a single command of the Father of Therns. I shall stay here until I rot if he does not return to bid me elsewhere."

Lakor's companion shook his head.

"You are my superior," he said; "I cannot do other than you sanction, though I still believe that we are foolish to remain."

I, too, thought that they were foolish to remain, for I saw from Woola's actions that the trail led through the room where the two therns held guard. I had no reason to harbor any considerable love for this race of self-deified demons, yet I would have passed them by were it possible without molesting them.

It was worth trying anyway, for a fight might delay us considerably, or even put an end entirely to my search—better men than I have gone down before fighters of meaner ability than that possessed by the fierce thern warriors.

Signaling Woola to heel I stepped suddenly into the room before the two men. At sight of me their long-swords flashed from the harness at their sides, but I raised my hand in a gesture of restraint.

"I seek Thurid, the black dator," I said. "My quarrel is with him, not with you. Let me pass then in peace, for if I mistake not he is as much your enemy as mine, and you can have no cause to protect him."

They lowered their swords and Lakor spoke.

"I know not whom you may be, with the white skin of a thern and the black hair of a red man; but were it only Thurid whose safety were at stake you might pass, and welcome, in so far as we be concerned.

"Tell us who you be, and what mission calls you to this unknown world beneath the Valley Dor, then maybe we can see our way to let you pass upon the errand which we should like to undertake would our orders permit."

I was surprised that neither of them had recognized me, for I thought that I was quite sufficiently well known either by personal experience or reputation to every thern upon Barsoom as to make my identity immediately apparent in any part of the planet. In fact, I was the only white man upon Mars whose hair was black and whose eyes were gray, with the exception of my son, Carthoris.

To reveal my identity might be to precipitate an attack, for every thern upon Barsoom knew that to me they owed the fall of their age-old spiritual supremacy. On the other hand my reputation as a fighting man might be sufficient to pass me by these two were their livers not of the right complexion to welcome a battle to the death.

To be quite candid I did not attempt to delude myself with any such sophistry, since I knew well that upon war-like Mars there are few cowards, and that every man, whether prince, priest, or peasant, glories in deadly strife. And so I gripped my long-sword the tighter as I replied to Lakor.

"I believe that you will see the wisdom of permitting me to pass unmolested," I said, "for it would avail you nothing to die uselessly in the rocky bowels of Barsoom merely to protect a hereditary enemy, such as Thurid, Dator of the First Born.

"That you shall die should you elect to oppose me is evidenced by the moldering corpses of all the many great Barsoomian warriors who have gone down beneath this blade—I am John Carter, Prince of Helium."

For a moment that name seemed to paralyze the two men; but only for a moment, and then the younger of them, with a vile name upon his lips, rushed toward me with ready sword.

He had been standing a little behind his companion, Lakor, during our parley, and now, ere he could engage me, the older man grasped his harness and drew him back.

"Hold!" commanded Lakor. "There will be plenty of time to fight if we find it wise to fight at all. There be good reasons why every thern upon Barsoom should yearn to spill the blood of the blasphemer, the sacrilegist; but let us mix wisdom with our righteous hate. The Prince of Helium is bound upon an errand which we ourselves, but a moment since, were wishing that we might undertake.

"Let him go then and slay the black. When he returns we shall still be here to bar his way to the outer world, and thus we shall have rid ourselves of two enemies, nor have incurred the displeasure of the Father of Therns."

As he spoke I could not but note the crafty glint in his evil eyes, and while I saw the apparent logic of his reasoning I felt, subconsciously perhaps, that his words did but veil some sinister intent. The other thern turned toward him in evident surprise, but when Lakor had whispered a few brief words into his ear he, too, drew back and nodded acquiescence to his superior's suggestion.

"Proceed, John Carter," said Lakor; "but know that if Thurid does not lay you low there will be those awaiting your return who will see that you never pass again into the sunlight of the upper world. Go!"

During our conversation Woola had been growling and bristling close to my side. Occasionally he would look up into my face with a low, pleading whine, as though begging for the word that would send him headlong at the bare throats before him. He, too, sensed the villainy behind the smooth words.

Beyond the therns several doorways opened off the guardroom, and toward the one upon the extreme right Lakor motioned.

"That way leads to Thurid," he said.

But when I would have called Woola to follow me there the beast whined and held back, and at last ran quickly to the first opening at the left, where he stood emitting his coughing bark, as though urging me to follow him upon the right way.

I turned a questioning look upon Lakor.

"The brute is seldom wrong," I said, "and while I do not doubt your superior knowledge, Thern, I think that I shall do well to listen to the voice of instinct that is backed by love and loyalty."

As I spoke I smiled grimly that he might know without words that I distrusted him.

"As you will," the fellow replied with a shrug. "In the end it shall be all the same."

I turned and followed Woola into the left-hand passage, and though my back was toward my enemies, my ears were on the alert; yet I heard no sound of pursuit. The passageway was dimly lighted by occasional radium bulbs, the universal lighting medium of Barsoom.

These same lamps may have been doing continuous duty in these subterranean chambers for ages, since they require no attention and are so compounded that they give off but the minutest of their substance in the generation of years of luminosity.

We had proceeded for but a short distance when we commenced to pass the mouths of diverging corridors, but not once did Woola hesitate. It was at the opening to one of these corridors upon my right that I presently heard a sound that spoke more plainly to John Carter, fighting man, than could the words of my mother tongue—it was the clank of metal—the metal of a warrior's harness—and it came from a little distance up the corridor upon my right.

Woola heard it, too, and like a flash he had wheeled and stood facing the threatened danger, his mane all abristle and all his rows of glistening fangs bared by snarling, backdrawn lips. With a gesture I silenced him, and together we drew aside into another corridor a few paces farther on.

Here we waited; nor did we have long to wait, for presently we saw the shadows of two men fall upon the floor of the main corridor athwart the doorway of our hiding place. Very cautiously they were moving now—the accidental clank that had alarmed me was not repeated.

Presently they came opposite our station; nor was I surprised to see that the two were Lakor and his companion of the guardroom.

They walked very softly, and in the right hand of each gleamed a keen long-sword. They halted quite close to the entrance of our retreat, whispering to each other.

"Can it be that we have distanced them already?" said Lakor.

"Either that or the beast has led the man upon a wrong trail," replied the other, "for the way which we took is by far the shorter to this point—for him who knows it. John Carter would have found it a short road to death had he taken it as you suggested to him."

"Yes," said Lakor, "no amount of fighting ability would have saved him from the pivoted flagstone. He surely would have stepped upon it, and by now, if the pit beneath it has a bottom, which Thurid denies, he should have been rapidly approaching it. Curses on that calot of his that warned him toward the safer avenue!"

"There be other dangers ahead of him, though," spoke Lakor's fellow, "which he may not so easily escape—should he succeed in escaping our two good swords. Consider, for example, what chance he will have, coming unexpectedly into the chamber of—"

I would have given much to have heard the balance of that conversation that I might have been warned of the perils that lay ahead, but fate intervened, and just at the very instant of all other instants that I would not have elected to do it, I sneezed.

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