"Kathakt will raise my children as heroes. He will teach them arms, and arm them well, and when they are old enough he will turn them loose to conquer their own lands. They will be no threat to his own domains, you see, and they will stand a good chance to survive if I do not return. I left Kathakt my flashlight-laser."

"Good enough."

"I hope so."

"Are we through with the Map of Kzin?"

Chmeee pondered. "I captured an aircraft pilot. They are all n.o.bility, with names and comprehensive educations. Chjarrl told me much about the age of exploration after I mocked the accomplishments of his ancestors. We may a.s.sume that there is an extensive historical library within the Behemoth. Shall we capture it?"

"Tell me what Chjarrl told you. How far did they get on Mars?"

"They found a wall of falling water. Later generations invented pressure suits and high-alt.i.tude aircraft. They explored the edges of the Map, and one team reached the center, where there was ice."

"I think we'll just skip the Behemoth's library, then. They never got inside. Hindmost, are you there?"

A microphone said, "Yes, Louis."

"We're heading for the Map of Mars. You do the same, but stay to port of us in case we have to flick across."

"Aye, aye. Have you anything to report?"

"Chmeee picked up some information. Kzinti explored the surface of the Map of Mars, and they didn't find anything un-Marslike. So we still don't know where to look for an opening."

"Perhaps from beneath."

"Yeah, could be. That'd be annoying. How are our guests holding out?"

"You should rejoin them soon."

"Soon as I can, then. You see if there's data on Mars in Needle's computer. And on martians. Louis out." He turned. "Chmeee, do you want to fly this thing? Don't exceed four miles per second."

The lander surged up and forward in obedience to the kzin's touch. A gray wall of cloud broke to let them through; then there was only blue sky, darkening as they rose. The Map of Kzin streamed below them. Then behind them.

Chmeee said, "The puppeteer seems docile enough."

"Yeah."

"You seem very sure of the Map of Mars."

"Yeah." Louis grinned. "It's a very nice piece of misdirection, but it couldn't be perfect, could it? They had too much to hide, by volume. We went under the Great Ocean on the way here. Guess what we found when we went under the Map of Mars?"

"Don't play games."

"Nothing. Nothing but sea bottom. Not even radiator fins. Most of the other Maps have radiator fins to cool the poles. Pa.s.sive cooling systems. There has to be a system to cool the Map of Mars. Where's the heat going? I thought it might be going into the sea water, but it wasn't. We think the heat is pumped directly into the superconductor grid in the Ringworld floor."

"Superconductor grid?"

"Big mesh, but it controls magnetic effects in the Ringworld foundation. It's used to control effects in the sun. If the Map of Mars plugs into the grid, it has to be the Ringworld control center."

Chmeee thought it over. He said, "They could not pump heat into the sea water. The warm, wet air would rise. Cloud patterns would stream inward and outward from great distances. From s.p.a.ce the Map of Mars would appear as a great target. Can you imagine Pak protectors making such a mistake?"

"No." Though Louis would have.

"I remember too little about Mars. The planet was never very important to your people, was it? It was no more than a source of legends. I do know that the Map is twenty miles high, to mimic the very rarefied air of the planet."

"Twenty miles high, and fifty-six million square miles in area. That's one billion, one hundred and twenty million cubic miles of hiding place."

"Urrr," said Chmeee. "You must be right. The Map of Mars is the Repair Center, and the Pak did their best to hide it. Chjarrl told me of the monsters and the storms and the distances of the Great Ocean. They would have made good pa.s.sive guardians. A fleet of invaders might never have guessed the secret."

Louis rubbed absently at four itching spots across his eyebrows. "One point twelve times ten to the ninth cubic miles. I have to admit it, that number leaves me numb. What were they keeping in there? Patches big enough to plug Fist-of-G.o.d Mountain? Machinery big enough to carry those patches, and plant them, and weld them tight? That winching equipment we saw on the rim wall, for the att.i.tude jets? Spare att.i.tude jets? Tanj, I'd love to find spare att.i.tude jets. But they'd still have room to spare."

"War fleets."

"Yeah. We already know about their big weapon, but-war fleets, of course, and ships to carry refugees, too. Maybe the whole Map is one big refugee ship. It must have been big enough to evacuate the Ringworld before the population started filling every niche in the ecology."

"A s.p.a.cecraft? Perhaps a s.p.a.cecraft big enough to tow the Ringworld back into place? I have trouble thinking on this scale, Louis."

"Me too. I don't think it'd be big enough."

"Then what did you have in mind when you destroyed our hyperdrive motor?" Suddenly the kzin was snarling.

Louis chose not to flinch. "I thought the Ringworld might be set up to act on the sun magnetically. I was almost right. The trouble-"

The Hindmost's voice blared from a speaker. "Louis! Chmeee! Set the lander on autopilot and flick across to me now!"

Chapter 29 -.

The Map of Mars Chmeee reached the disc ahead of Louis, in one monstrous bound. The kzin could take orders too, Louis thought. He forbore to remark on the fact.

The City Builders were looking out through the hull, not at the pa.s.sing seascape-which was nothing but blue sea and cloud-striped blue sky merging at the infinity-horizon-but at a movie-screen-sized hologram. As Chmeee appeared on the receiver disc they turned and flinched and then tried to hide it.

Louis said, "Chmeee, meet Harkabeeparolyn and Kawaresksenjajok, librarians from the floating city. They've been of great help in gaining us information."

The kzin said, "Good. Hindmost, what is the problem?"

Louis tugged at the kzin's fur and pointed.

"Yes," said the puppeteer. "The sun."

The sun showed dimmed and magnified in the hologram rectangle. A brilliant patch near the center was shifting, twisting, changing shape as they watched.

Chmeee said, "Wasn't the sun doing that shortly before we boarded the s.p.a.ceport ledge?"

"Right. You're looking at the Ringworld meteor defense. Hindmost, what do we do now? We can slow down, but I don't see any way to save the lander."

"My first thought was to save your valuable selves," the puppeteer said.

The sea threw back a highlight from directly below the fleeing Needle. Now it seemed to be growing brighter, with a violet tinge. Suddenly, momentarily, it was unbearably bright. Then it was a black spot on the hull beneath their feet.

And a thread of jet-black, outlined in violet-white, stood upon the spinward horizon. A vertical pillar, reaching from ground to sky. Above the atmosphere it was invisible.

The kzin spoke words in the Hero's Tongue.

"All very well," said the Hindmost in Interworld, "but what is it firing on? I a.s.sumed we were the target."

Louis asked, "Isn't the Map of Earth in that direction?"

"Yes. Also a good deal of water and considerable Ringworld landscape."

Where the beam touched down, the horizon glowed white. Chmeee whispered in the Hero's Tongue, but Louis caught the sense. "With such a weapon I could boil the Earth to vapor."

"Shut up."

"It was a natural thought, Louis."

"Yeah."

The beam cut off abruptly. Then it touched down again, a few degrees to port.

"Tanj dammit! All right, Hindmost, take us up. Take us high enough to use the telescope."

There was a glowing yellow-white point on the Map of Earth. It had the look of a major asteroid strike.

There was a similar glow farther away, at the far sh.o.r.e of the Great Ocean.

The solar flare had dimmed and was losing coherence.

Chmeee asked, "Were there aircraft or s.p.a.cecraft in those directions? Fast-moving objects?"

"The instruments may have recorded something," the Hindmost said.

"Find out. And take us down to one mile alt.i.tude. I think we want to approach the Map of Mars from below the surface."

"Louis?"

"Do it."

Chmeee asked, "Have you knowledge of how that laser beam was produced?"

"Louis can tell you," the puppeteer said. "I will be busy."

Needle and the lander converged on the Map of Mars from two directions. The Hindmost held the two vehicles parallel so that it was possible to cross between them.

Louis and Chmeee flicked across to the lander for lunch. Chmeee was hungry. He consumed several pounds of red meat, a salmon, a gallon of water. Louis's own appet.i.te suffered. He was pleased that his guests weren't watching.

"I don't understand why you picked up these pa.s.sengers," Chmeee said, "unless it was to mate with the woman. But why the boy?"

"They're City Builders," Louis said. "Their species ruled most of the Ringworld. And I plucked these two out of a library. Get to know them, Chmeee. Ask them questions."

"They fear me."

"You're a soft-spoken diplomat, remember? I'm going to invite the boy to see the lander. Tell him stories. Tell him about Kzin and hunting parks and the House of the Patriarch's Past. Tell him how kzinti mate."

Louis flicked across to Needle, spoke to Kawaresksenjajok, and was back in the lander with him before Harkabeeparolyn quite realized what was happening.

Chmeee showed him how to fly. The lander swooped and did somersaults and darted skyward at his command. The boy was entranced. Chmeee showed him the magic of binocular goggles, and superconductor cloth, and impact armor.

The boy asked about kzinti mating practices.

Chmeee had mated with a female who could talk! It had opened new vistas for him. He told Kawaresksenjajok what he wanted to know-which Louis thought was pretty dull stuff-and then got the boy talking about mating and rishathra.

Kawaresksenjajok had no practice but a lot of theory. "We make records if a species will let us. We have archives of tapes. Some species have things they can do instead of rishathra, or they may like to watch or to talk about it. Some mate in only one position, others only in season, and this carries over. All of this influences trade relationships. There are aids of various kinds. Did Luweewu tell you about vampire perfume?"

They hardly noticed when Louis left to return to Needle alone.

Harkabeeparolyn was upset. "Luweewu, he might hurt Kawa!"

"They're doing fine," Louis told her. "Chmeee's my crewmate, and he likes children of all species. He's perfectly safe. If you want to be his friend too, scratch him behind the ears."

"How did you hurt your forehead?"

"I was careless. Look, I know how to calm you down."

They made love-well, rishathra-on the water bed, with the ma.s.sage unit going. The woman might have hated Panth Building, but she had learned a good deal. Two hours later, when Louis was sure he would never move again, Harkabeeparolyn stroked his cheek and said, "My time of mating should end tomorrow. Then you may recover."

"I have mixed feelings about that." He chuckled.

"Luweewu, I would feel better if you would rejoin Chmeee and Kawa."

"Okay. Behold as I stagger to my feet. See me at the stepping disc? There I go: poof, gone."

"Luweewu-"

"Oh, all right."

The Map of Mars was a dark line, growing, becoming a wall across their path. As Chmeee slowed, microphones on the lander's hull picked up a steady whispering, louder than the wind of their pa.s.sage.

They came to a wall of falling water.

From a mile distant it appeared perfectly straight and infinitely long. The top of the waterfall was twenty miles above their heads. The base was hidden in fog. Water thundered in their ears until Chmeee had to turn off the microphones, and then they could hear it through the hull.

"It's like the water condensers in the city," the boy said. "This must be where my people learned how to make water condensers. Chmeee, did I tell you about water condensers?"