So I had walked into a city of five hundred houses and seen only an expanse of open beach beside a restless sea.

"But where are the people?" I asked. "Are they, too, invisible?"

"Those who are not away, hunting or fishing, are in their homes," explained O Ala. "We do not venture out any more than is necessary, lest Morgors be cruising around in their invisible ships and see us; thus discovering our city."

"If any of us should be thus caught out," said Han Du, "he must run away from the city as fast as he can, for if he entered a house, the Morgors would immediately know that there was a city here. It is the sacrifice that each of us is in honor bound to make for the safety of all, for he who runs is almost invariably caught and carried away, unless he chooses to fight and die."

"Tell me," I said to Han Du, "how in the world you found your house, when you could not see it or any other house."

"You noticed the umpalla plants growing throughout the city?" he asked.

"I noticed some plants, but I saw no city."

They both laughed again. "We are so accustomed to it that it does not seem at all strange to us," said O Ala, "but I can understand that it might prove very confusing to a stranger. You see, each plant marks the location of a house. By long experience, each of us has learned the exact location of every house in the city in relation to every other house."

I remained for what may have been five or six days of earth time in the home of Han Du and O Ala. I met many of their friends, all of whom were gracious and helpful to me in every way that they could be. I was furnished with maps of considerable areas of the planet, parts of which, I was told, were still unexplored even by the Morgors. Of greatest value to me was the fact that Zanor appeared on one of the maps, which also showed that a vast ocean lay between me and the country in which I believed Dejah Thoris to be. How I was to cross this ocean neither I nor my new found friends could offer a suggestion, other than the rather mad scheme I envisioned of building a sail boat and trusting myself to the mad caprices of an unknown sea perhaps swarming with dangerous reptiles. But this I at last decided was the only hope I had for being again reunited with my princess.

There was a forest several miles along the coast from the city, where I might hope to find trees suitable for the construction of my craft. My friends tried their best to dissuade me; but when they found that I was determined to carry out my plan, they loaned me tools; and a dozen of them volunteered to accompany me to the forest and help me build my boat.

At last all was in readiness; and, accompanied by my volunteer helpers, I stepped from the house of Han Du to start the short march to the forest.

Scarcely were we in the open when one of my companions cried, "Morgors!" Whereupon the Savators scattered in all directions away from their city.

"Run, John Carter!" shouted Han Du, but I did not run. A few yards distant, I saw the open doorway in the side of an invisible ship; and I saw six or seven Morgors emerge from it. Two rushed toward me; the others scattered in pursuit of the Savators. In that instant a new plan flashed across my mind. Hope, almost extinct leaped to life again.

I whipped my sword from its scabbard and leaped forward to meet the first of the oncoming Morgors, thanking God that there were only two of them, as delay might easily wreck my hopes. There was no finesse in my attack: it was stark, brutal murder; but my conscience did not bother me as I drew my sword from the heart of the first Morgor and faced the second.

The second fellow gave me a little more trouble, as he had been forewarned by the fate of his companion; and, too, he presently recognized me. That made him doubly wary. He commenced to howl to the others, who were pursuing the Savators, to come back and help him, bellowing that here was the creature from Garobus who had led the slaughter at the graduating exercises. From the corner of an eye, I saw that two of them had heard and were returning. I must hurry!

The fellow now fought wholly on the defensive in order to gain time for the others to join him. I had no mind to permit this, and I pressed him hard, often laying myself wide open, a great swordsman could have killed me easily. At last I reached him with a mighty cut that almost severed his head from his body; then, with only a quick glance behind me to see how close the others were, I leaped toward the open doorway of the otherwise invisible ship, a Morgor close upon my heels.

With naked blade still in my hand, I sprang aboard and closed the door behind me; then I wheeled to face whatever of their fellows had been left aboard to guard the craft. The fools had left no one. I had the ship all to myself; and as I ran to the controls I heard the Morgors beating upon the door, angrily demanding that I open it. They must have taken me for a fool, too.

A moment later the ship rose into the air, and I was away upon one of the strangest adventures of my life-navigating an unknown planet in an invisible craft. And I had much to learn about navigation of Jupiter. By watching Vorion, I had learned how to start and stop a Morgor ship, how to gain or lose altitude, and how to cloak the ship in invisibility; but the instruments upon the panel before me were all entirely meaningless to me. The hieroglyphs of the Morgors were quite unintelligible. I had to work it all out for myself. Opening all the ports, I had a clear field of vision. I could see the shore I had just left, and I knew the direction of the coast line. Han Du had explained this to me. It ran due north and south at that point. The ocean lay to the west of it. I found an instrument which might easily have been a compass; when I altered the course of the ship, I saw that it was a compass. I now had my bearings as closely as it was possible for me to get them. I consulted my map and discovered that Zanor lay almost exactly southeast; so out across that vast expanse of ocean I turned the prow of my ship.

I was free. I had escaped the Morgors unharmed. In Zanor, Dejah Thoris was safe among friends. That I should soon be with her, I had no doubt. We had experienced another amazing adventure. Soon we should be reunited. I had not the slightest doubt of my ability to find Zanor. Perhaps it is because I am always so sure of myself that I so often accomplish the seemingly impossible.

How long I was in crossing that dismal ocean, I do not know. With Jupiter whirling on its axis nearly three times as fast as earth, and with no sun, moon, nor stars, I could not measure time.

I saw no ship upon that entire vast expanse of water, but I did see life-plenty of it. And I saw terrific storms that buffeted my craft, tossing it about like a feather. But that was nothing compared with what I saw below me as the storms at me height of their fury lashed the surface of the waters. I realized then how suicidal would have been my attempt to cross that terrible ocean in the frail craft that I had planned to build. I saw waves that must have measured two hundred feet from trough to crest-waves that hurled the mighty monsters of the deep as though they had been tiny minnows. No ship could have lived in such seas. I realized then why I saw no shipping on this great Jupiterian ocean.

But at last I sighted land ahead-and what land! Zan Dar had told me of the mighty mountains of Zanor rearing their forested heads twenty miles above the level of the sea, and it was such mountains that lay ahead of me. If I had reckoned accurately, this should be Zanor; and these breath-taking mountains assured me that I had not gone wrong.

I knew from Zan Dar's explanation just where to search for the stamping grounds of his tribe-a wild mountain tribe of fighting men. They lay in a land of meadows and ravines on the east slope of the highest mountain and at an altitude of only about ten miles, or about halfway to the summit. Here the air is only slightly thinner than at sea level, as the cloud envelope retains the atmosphere of Jupiter as though it were held in a bag, permitting none of it to escape, while the rapid revolution of the planet tends to throw the atmosphere far up from the surface.