As the clouds turned black the dim street lamps were lighted. There were lights in most of the houses. Toh and Guy threaded the crowds and attracted little attention. Soon they came to wider, deserted streets: A steady upward ascent out of the broad circular bowl, spread like a flat cauldron upon the inner slopes of which the city was built.

The street they followed was soon a wide ascending road, with spreading tree branches interlocking overhead; low stone houses at the sides, set in verdant gardens or patches of cultivated soil.

With the lesser gravity of Mercury, Guy could have run leaping like a faun. But he did not want to attract undue attention. He held Toh by the hand, pulling him up the steep incline of the street. The houses were soon farther apart. Less soil was here; the metallic, barren desert land began showing. The street dwindled and was lost at the summit. Ahead was a tumbled region of pointed crags and strewn bouldersan upland desert plateau stretching away into the darkness with the black sullen clouds hanging low above the encircling hills. This was the highland from which the Hill City took its name.

They reached the rim. Behind them the bowl of the city lay with winking tiny lights like myriad eyes. Ahead there was a small level space strewn with boulders.

Guy gestured. "That's where you told her?"

"Yes." They stood at the brink of a small canyon, a rift in the coppery rocks. It was some thirty feet wide and equally deep.

Guy smiled at his companion. "I can't help you over, Tob."

"No. I will climb down and across it." He started clambering laboriously down the broken side of the rift. Guy walked back, came with a rush, and leapedsailed in a flat arc with spread arms for balance and legs hunched up, and landed well across the rift, where he stood waiting for Toh. The Mercurian climbed up, panting.

"Not in sight yet, Guy?"

"Noyes, there they are." The platform came sailing from over the city. A small rectangle, fifteen feet long by half as wide. Like a small raft, built of split, porous treetrunks, lashed together with ropes of vines. It had six-foot handlessticks projecting out from its sides. At each of them a girl was flying, five on either side. The platform passed in a low circle, came down and landed on the rocks.

The two men ran to it. The platform had a low, foot-high railing surrounding it, with handles to which the riders might cling. The girl Aina was crouched there.

"We are ready, Guy. They would not let me fly. I am tired; they said I would hold them back. May I go with you? They will not mind my little extra weight." The ten girls stood, eager with questionsa flood of them buried In their native tongue at Toh. He waved them aside. The girls -were all barely maturedred-feathered and blue-feathered wings, black and gold-haired. They stopped their questioning, and stood alert and grim. Little warriors.

The thought struck Guy and made him shudder. Frail, beautiful little creatures, these flying virgins of Mercury.

For them to be embarked on deeds of violence seemed utterly unjust. Yet, with a flash of vision, Guy saw what was coming.

The girls realized it well enough. Their landfairest region of the universe to themwas threatened now by an alien race. They had had differences with their own government and had rebelled. But that was forgotten now in the greater peril.

Guy was saying, "Yes, you may go with us, Aina. Ready, now."

"" The three of them were on the platform. Guy gave the command, told the girls the direction. The girls raised the platform by the handles, stooped a trifle, and in unison, at a word from their leader, leaped into the air. With wings beating rhythmically. With stroke set by the two leading girls, they sailed off toward the Water City.

To Guy, lying on the platform, it seemed an interminable flight. Yet in actual time it was not longhardly more than an hour. The low, sullen clouds formed a leaden canopy overhead. The platform sailed level, creating its own wind in the heavy, sultry air.

A thousand feet below it, the bleak landscape rolled steadily backward. Copper desert. Sheets of bumished, wavy surface like a strange shining sea rippled by a breeze and frozen to immobility. Again it was broken by canyons.

Sheer walls; a mist of vapor sometimes at their feet. There were small valleys, with water and soil and a little struggling vegetation. Others, incongruously luxuriant, with a rank, exotic, tropical growth.

There had been occasional huts, tiny clusters nearly always where the vegetation existed. Moundlike stone huts, here the half-nomadic rural population of the Light Country fought for meager existence. They were all deserted now.

Girls had flown past with news of the invasion.

From the platform occasional refugees were visiblelittle groups foiling along, sometimes attended by a few young girls flying low above them. There was no sign of the enemy.

From here the valley of the Water City lay concealed behind the rim line of tumbled peaks with the precipice brink beyond them. As Guy had hoped, the semidarkness held; it had even grown dimmer. A deep twilight gloom now, through which the distant peaks were appearing, blurred against the solid dark sky. The girls were tired, but they still flew in steady, orderly fashion.

"They were on this side when I left," murmured Aina.

"On the heights. The attack was over, I think."

"But the main body of them were on the other slopes?" Guy demanded. "Beyond the marshes?"

"Yes. From these peaks they were going down to join the others. It was all so blurred. Smoke clouds, fumes, burning houses, smoke everywhere... ." She shuddered. "I could not see much, so I did not know what was happening. I saw the silver ball go past." She stared with eyes that now had no hint of tears. "I want now only to rescue Tama. To follow her, fighting these men who killed my Jal." And she was only fifteen, with childhood barely passed! "None are down there now," said Toh. "No one along the _~.-_ ** nm.

Blurred and dim, the wrecked Water City lay smoldering in the night shadows of the valley. Vapors still hung upon it, and the heavy silence of death. Shadows down there concealed the drab aftermath of a thousand horrors.

Occasional little red-yeJlow flames glowed, where charred, still luminous embers of wreckage lay strewn on the water.

The platform ascended, passed to one side over the dark and silent marshes, higher over deserted terraces, swept beyond the farther uplands. The invaders had been here; but they were not here now. From this height, down through the gloom, there was no sign of any living thing remaining.

"Well, that's the end of that," said Guy. Disappointment flooded him. A few short hours before, Tama had doubtless been here. But now she was gone.

It seemed obvious that the ball and one portion of the Cold Country army had met here, and now had withdrawn.

The invaders, having destroyed the Water City, were waiting before attacking further. To follow them with the platform back toward the Cold Country seemed to Guy a useless undertaking. Yet he dallied with it, even though he knew his better course was to return at once to the Hill City, tell Grenfell the condition, and join the Flying Cube.

Toh had turned them back, directly over the wreckage of the city. They flew lower, by whatever chance of fate, Guy never knew. He was deep in his gloomy thoughts. Toh was silent, waiting for Guy's orders. Aina told the girls to return.

The platform went down in a long swoop. Guy came to himself, to see that they were barely two hundred feet above the water. The acrid smell of gases, smoke of charring embers, enveloped them. A turgid, rushing darkness.

Close under them, Guy made out what had been a street: sullen, oily water strewn with mangled houses; naked, blackened treetrunks standing like sticks with dark, torn ribbons of shriveled vegetation dangling from them.