The evident cordiality with which the two men exchanged greetings filled me with wonder, for the black and white men of Barsoom were hereditary enemies-nor ever before had I known of two meeting other than in battle.

Evidently the reverses that had recently overtaken both peoples had resulted in an alliance between these two individuals-at least against the common enemy-and now I saw why Thurid had come so often out into the Valley Dor by night, and that the nature of his conspiring might be such as to strike very close to me or to my friends.

I wished that I might have found a point closer to the two men from which to have heard their conversation; but it was out of the question now to attempt to cross the river, and so I lay quietly watching them, who would have given so much to have known how close I lay to them, and how easily they might have overcome and killed me with their superior force.

Several times Thurid pointed across the river in my direction, but that his gestures had any reference to me I did not for a moment believe. Presently he and Matai Shang entered the latter's boat, which turned out into the river and, swinging round, forged steadily across in my direction.

As they advanced I moved my boat farther and farther in beneath the overhanging wall, but at last it became evident that their craft was holding the same course. The five paddlers sent the larger boat ahead at a speed that taxed my energies to equal.

Every instant I expected to feel my prow crash against solid rock. The light from the river was no longer visible, but ahead I saw the faint tinge of a distant radiance, and still the water before me was open.

At last the truth dawned upon me-I was following a subterranean river which emptied into the Iss at the very point where I had hidden.

The rowers were now quite close to me. The noise of their own paddles drowned the sound of mine, but in another instant the growing light ahead would reveal me to them.

There was no time to be lost. Whatever action I was to take must be taken at once. Swinging the prow of my boat toward the right, I sought the river's rocky side, and there I lay while Matai Shang and Thurid approached up the center of the stream, which was much narrower than the Iss.

As they came nearer I heard the voices of Thurid and the Father of Therns raised in argument.

"I tell you, Thern," the black dator was saying, "that I wish only vengeance upon John Carter, Prince of Helium. I am leading you into no trap. What could I gain by betraying you to those who have ruined my nation and my house?"

"Let us stop here a moment that I may hear your plans," replied the hekkador, "and then we may proceed with a better understanding of our duties and obligations."

To the rowers he issued the command that brought their boat in toward the bank not a dozen paces beyond the spot where I lay.

Had they pulled in below me they must surely have seen me against the faint glow of light ahead, but from where they finally came to rest I was as secure from detection as though miles separated us.

The few words I had already overheard whetted my curiosity, and I was anxious to learn what manner of vengeance Thurid was planning against me. Nor had I long to wait. I listened intently.

"There are no obligations, Father of Therns," continued the First Born. "Thurid, Dator of Issus, has no price. When the thing has been accomplished I shall be glad if you will see to it that I am well received, as is befitting my ancient lineage and noble rank, at some court that is yet loyal to thy ancient faith, for I cannot return to the Valley Dor or elsewhere within the power of the Prince of Helium; but even that I do not demand-it shall be as your own desire in the matter directs."

"It shall be as you wish, Dator," replied Matai Shang; "nor is that all-power and riches shall be yours if you restore my daughter, Phaidor, to me, and place within my power Dejah Thoris, Princess of Helium.

"Ah," he continued with a malicious snarl, "but the Earth man shall suffer for the indignities he has put upon the holy of holies, nor shall any vileness be too vile to inflict upon his princess. Would that it were in my power to force him to witness the humiliation and degradation of the red woman."

"You shall have your way with her before another day has passed, Matai Shang," said Thurid, "if you but say the word."

"I have heard of the Temple of the Sun, Dator," replied Matai Shang, "but never have I heard that its prisoners could be released before the allotted year of their incarceration had elapsed. How, then, may you accomplish the impossible?"

"Access may be had to any cell of the temple at any time," replied Thurid. "Only Issus knew this; nor was it ever Issus' way to divulge more of her secrets than were necessary. By chance, after her death, I came upon an ancient plan of the temple, and there I found, plainly writ, the most minute directions for reaching the cells at any time.

"And more I learned-that many men had gone thither for Issus in the past, always on errands of death and torture to the prisoners; but those who thus learned the secret way were wont to die mysteriously immediately they had returned and made their reports to cruel Issus."

"Let us proceed, then," said Matai Shang at last. "I must trust you, yet at the same time you must trust me, for we are six to your one."

"I do not fear," replied Thurid, "nor need you. Our hatred of the common enemy is sufficient bond to insure our loyalty to each other, and after we have defiled the Princess of Helium there will be still greater reason for the maintenance of our allegiance-unless I greatly mistake the temper of her lord."

Matai Shang spoke to the paddlers. The boat moved on up the tributary.

It was with difficulty that I restrained myself from rushing upon them and slaying the two vile plotters; but quickly I saw the mad rashness of such an act, which would cut down the only man who could lead the way to Dejah Thoris' prison before the long Martian year had swung its interminable circle.

If he should lead Matai Shang to that hollowed spot, then, too, should he lead John Carter, Prince of Helium.

With silent paddle I swung slowly into the wake of the larger craft.

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.