"That's a good place. Don't try to fly it. Just turn on every sensor on the probe, and every sensor aboard Needle and the lander. Turn most of them in the direction of the shadow squares. Now, where else would you put a meteor defense? Bear in mind that it can't seem to fire at anything under the Ringworld floor."

"I have no ideas."

"Okay. We aim cameras all over the Arch. Cameras on the shadow squares. Cameras on the sun. Cameras on the Map of Kzin and the Map of Mars."

"Definitely."

"We stay at an alt.i.tude of a thousand miles. Shall we dismount the probe in the cargo hold? Set it to following us?"

"Our only source of fuel? No."

"Then start accelerating until something happens. How does it sound?"

"Aye, aye," said the Hindmost, and he turned to the controls. And Louis, who would have welcomed more discussion, more time to nerve himself up, kept his silence.

The cameras caught it, but none of Needle's pa.s.sengers did. Even if they'd been looking up, they wouldn't have caught it. They would have seen glare-white stars and the checkered blue Arch glowing against black s.p.a.ce, and a black circle at the peak of the Arch, where Needle's flare shielding blocked out the naked sun.

But they weren't even looking up.

Below the ruin of the hyperdrive motor, the land was green with life. Jungle and swamp and wild land prevailed, with an occasional ragged crazy quilt of cultivated farmland. Of the Ringworld hominids they'd seen so far, not many would make farmers.

There were covies of boats on flat seas. Once they crossed a spider web of roads half an hour wide, seven thousand miles wide. The telescope showed steeds carrying riders or pulling small carts. No powered vehicles. A City Builder culture must have fallen here, and stayed down.

"I feel like a G.o.ddess," Harkabeeparolyn said. "n.o.body else could have such a view."

"I knew a G.o.ddess," Louis said. "At least she thought she was. She was a City Builder too. She was part of a s.p.a.cecraft crew; she probably saw what you're seeing now."

"Ah."

"Don't let it go to your head."

Fist-of-G.o.d Mountain shrank slowly. The Earth's moon could have nestled in that vast sh.e.l.l. One had to see the mountain over such a distance, standing behind a landscape vaster than the habitable surfaces of all the worlds of known s.p.a.ce, to appreciate its size. Louis wasn't feeling G.o.dlike. He felt tiny. Vulnerable.

The autodoc lid aboard the lander hadn't moved. Louis asked, "Hindmost, could Chmeee have had other wounds?"

The puppeteer was out of sight somewhere, but his voice came clear. "Of course."

"He could be dying in there."

"No. Louis, I'm busy. Don't bother me!"

The telescope view had become a blur. The bright land a thousand miles below was visibly moving now; Needle's velocity had pa.s.sed five miles per second. Orbital speed for Earth.

Cloud decks shone bright enough to hurt the eyes. Far aft, a checkerboard pattern of cultivation was thinning out. Directly below, the land dipped, then leveled off into hundreds of miles of flat gra.s.sland. The flatlands extended to right and left as far as the eye could see. Rivers that fed into the flats became swamps, suddenly green.

You could trace a ragged line of contoured bays, inlets, islands, peninsulas: the mark of Ringworld sh.o.r.eline, designed for the convenience of boats and shipping. But that was the spinward border. Then several hundred miles of flat, salt-poisoned land. Then the blue line of ocean. Louis felt the hair stir on his neck at this fresh memento of the Fist-of-G.o.d impact. Even this far away, the sh.o.r.eline of the Great Ocean had been lifted; the sea had receded seven or eight hundred miles.

Louis rubbed dazzled eyes. It was too bright down there. Violet highlights- Then blackness.

Louis closed his eyes tight. When he opened them it was as if he had left them closed: black as the inside of a stomach.

Harkabeeparolyn screamed. Kawaresksenjajok thrashed. His arm struck Louis's shoulder, and the boy gripped Louis's arm with both hands and hung on. The woman's scream cut off abruptly. Then she said, in a voice with teeth in it, "Luweewu, where are we?"

Louis said, "I take a wild guess and say we're at the bottom of the ocean."

"You are correct," said the Hindmost's contralto. "I have a good view by deep-radar. Shall I turn on a spotlight?"

"Sure."

The water was murky. Needle wasn't as deep as it might have been. There were fish nosing about; there was even a seaweed forest anch.o.r.ed nearby.

The boy released Louis and pressed his nose to the wall. Harkabeeparolyn stared too, but she was shivering. She asked, "Luweewu, can you tell me what happened? Can you make it make sense?"

"We'll find out," said Louis. "Hindmost, take us up. Back to a thousand miles alt.i.tude."

"Aye, aye."

"How long were we in stasis?"

"I cannot tell. Needle's chronometer stopped, of course. I will signal the probe to send data, but the lightspeed delay is sixteen minutes."

"How fast were we moving?"

"Five point eight one miles per second."

"Then take us up to five even and hold us there while we see what we've got."

The signals from the lander resumed as Needle approached the surface. Fire still surrounded the lander. The autodoc was still closed. Chmeee should have emerged by now, Louis thought.

Blue light grew around them. Needle broke free of the ocean and surged upward into sunlight. The deck barely quivered as the ocean dropped away at twenty gravities of acceleration.

The view aft was instructive.

Forty or fifty miles behind them, huge combers rolled across the flat beach that had been an undersea continental shelf. A grooved line ran straight back from the sh.o.r.e. Needle had not struck water The fireball had struck land and kept going.

Farther back, the beach became gra.s.sland. Farther yet, forest. It was all burning. Thousands of square miles of firestorm, flame streaming inward from all sides, pouring straight upward in the center, like the steam rushing in over a sunflower patch far, far away. Needle's impact could not have caused all of that.

"Now we know," the Hindmost said. "The meteor defense is programmed to fire on inhabited territory. Louis, I am awed. The power expended compares to nothing less than the project that set the Fleet of Worlds in motion. Yet the automatics must do this repeatedly."

"We know the Pak thought big. How was it done?"

"Don't bother me for a while. I'll let you know." The Hindmost disappeared.

It was annoying. The puppeteer had all the instruments. He could lie his heads off, and how would Louis know? At this point the puppeteer couldn't even change the arrangement ...

Harkabeeparolyn was tugging at his arm. He snapped, "What?"

"Louis, I don't ask this lightly. My sanity flinches. Forces batter me, and I can't even describe them. Please, what has happened to us?"

Louis sighed. "I'd have to tell you about stasis fields and the Ringworld meteor defense. Also about Pierson's puppeteers and General Products hulls and Pak."

"I am ready."

And he talked, and she nodded and asked questions, and he talked. He couldn't be certain how much she understood, and of course he himself knew a lot less than he wanted to. Mostly he was telling her that Louis Wu knew what he was talking about. And when she was sure of that, she became calmer, which was what he was after.

Presently she took him to the water bed-ignoring the presence of Kawaresksenjajok, who grinned at them over his shoulder, once, then went back to watching the Great Ocean move past.

In rishathra there was rea.s.surance. Spurious, perhaps. Who cared?

There sure was a lot of water down there.

From a thousand miles up, one could see a long way before the blanket of air blocked the view. And for most of that distance, there wasn't a single island! The contours of sea bottom showed, and some of that was shallow enough. But the only islands were far behind, and those had probably been underwater peaks before Fist-of-G.o.d distorted the land.

There were storms. One looked in vain for the spiral patterns that meant hurricane and typhoon. But there were cloud patterns that looked like rivers in the air. As you watched them, they moved: even from this height, they moved.

The kzinti who dared that vastness had not been cowards, and those who returned had not been fools. That pattern of islands on the starboard horizon-you had to squint to be sure it was really there-must be the Map of Earth. And it was lost in all that blue.

A cool, precise contralto voice eased into his thoughts. "Louis? I have reduced our maximum velocity to four miles per second."

"Okay." Four, five-who cared?

"Louis, where did you say the meteor defense was located?"

Something in the puppeteer's tone ... "I didn't say. I don't know."

"The shadow squares, you said. You're on record. It must be the shadow squares if the meteor defense can't guard the Ringworld's underside." No overtones, no emotion showing in that voice.

"Do I gather I was wrong?"

"Now, pay attention, Louis. As we pa.s.sed four point four miles per second, the sun flared. I have it on visual record. We didn't see it because of the flare shielding. The sun extruded a jet of plasma some millions of miles long. It is difficult to observe because it came straight at us. It did not arch over in the sun's magnetic field, as flares commonly do."

"That was no solar flare that hit us."

"The flare stretched out several million miles over a period of twenty minutes. Then it lased in violet."

"Oh my G.o.d."

"A gas laser on a very large scale. The earth still glows where the beam fell. I estimate that it covered a region ten kilometers across: not an especially tight beam, but it would not normally need to be. With even moderate efficiency, a flare that large would power a gas laser beam at three times ten to the twenty-seventh power ergs per second, for on the order of an hour."

Silence.

"Louis?"

"Give me a minute. Hindmost, that is one impressive weapon." It hit him, then: the secret of the Ringworld engineers. "*That's* why they felt safe. That's why they could build a Ringworld. They could hold off any kind of invasion. They had a laser weapon bigger than worlds, bigger than the Earth-Moon system, bigger than ... Hindmost? I think I'm going to faint."

"Louis, we don't have time for that."

"What caused it? Something caused the sun to jet plasma. Magnetic, it has to be magnetic. Could it be one function of the shadow squares?"

"I wouldn't think so. Cameras record that the shadow square ring moved aside to allow the beam to pa.s.s, and constricted elsewhere, presumably to protect the land from increased insolation. We cannot a.s.sume that this same shadow-square ring was manipulating the photosphere magnetically. An intelligent engineer would design two separate systems."

"You're right. Absolutely right. Check it anyway, will you? We've recorded all possible magnetic effects from three different angles. Find out what made the sun flare." Allah, Kdapt, Brahma, Finagle, let it be the shadow squares! "Hindmost? Whatever you find, don't curl up on me."

There was a peculiar pause. Then "Under the circ.u.mstances, that would doom us all. I would not do that unless there was no hope left. What are you thinking?"

"There is never no hope left. Remember."

The Map of Mars was in view at last. It was farther away than the Map of Earth-a hundred thousand miles straight to starboard-but unlike the Map of Earth, it was one compact ma.s.s. From this angle it showed as a black line: twenty miles above the sea, as the Hindmost had predicted.

A red light blinked on the lander's instrument board. Temperature: a hundred and ten Fahrenheit, just right for a spa. No lights blinked on the big coffin that held Chmeee. The autodoc had its own temperature controls.

The kzinti defenders seemed to have run out of explosives. Their supply of firewood seemed infinite.

Twenty thousand miles to go, at four miles per second.

"Louis?"

Louis eased himself out of the sleeping field. The Hindmost, he thought, looked awful. Mane rumpled, the garnets rubbed off along one side. He staggered as if his knees were made of wood.

"We'll think of something else," Louis told him. He was wishing he could reach through the wall, stroke the puppeteer's mane, give rea.s.surance of some kind. "Maybe there's some kind of library in that castle. Maybe Chmeee already knows something we don't. Tanj, maybe the repair crew already knows the answer."

"We know the same answer. A chance to study sunspots from underneath." The puppeteer's voice was wintry-cool, the voice of a computer. "You guessed, didn't you? Hexagonal patterns of superconductor embedded in the Ringworld floor. The scrith can be magnetized to manipulate plasma jets in the solar photosphere."

"Yeah."

"It may have been just such an event that pushed the Ringworld off center. A plasma jet formed to fire on a meteoroid, a stray comet, even a fleet from Earth or Kzin. The plasma impacted the Ringworld. There were no att.i.tude jets to push it back into place. Without the plasma jet, the meteor itself might have been sufficient. The repair crew came later: too late."

"Let's hope not."

"The grid is not a backup for the att.i.tude jets."

"No. Are you all right?"

"No."

"What are you going to do?"

"I will follow orders."

"Good."

"If I were still Hindmost to this expedition, I would give up now."

"I believe you."

"Have you guessed the worst of it? I compute that the sun can probably be moved. The sun can be made to jet plasma, and the plasma can be made to act as a gas laser, forming a photon drive for the sun itself. The Ringworld would be pulled along by the sun's gravity. But even the maximum thrust would be minuscule, too little to help us. At anything over two times ten to the minus fourth power gravities of acceleration, the Ringworld would be left behind. In any case, radiation from the plasma jet would ruin the ecology. Louis, are you laughing?"

Louis was. "I never thought of moving the sun. I never would have. You actually went ahead and worked out the math?"