The Ringworld Engineers

and so did Louis Wu. Martians had been extinct in human space for hundreds of years.

The air was clear as vacuum. Off to starboard, well beyond the horizon, was a mountain taller than any on Earth. Mons Olympus, of course. And a splinter of white floated above the crater.

Needle fell, and pulled out of the fall just above the crescent dunes. The structure was still visible, floating fifty to sixty yards above the peak; and Needle must have been quite visible to its occupants.

“Chmeee?”

“Listening.”

Louis fought a tendency to whisper. “We’ve found a floating skyscraper. Maybe thirty stories tall, with bay windows and a landing ledge for cars. Built like a double cone. It looks very much like the building we took over on our first trip, the good ship Improbable.”

“Identical?”

“Not quite, but close. And it’s floating above the highest mountain on Mars, just like a god-tanjed signpost.”

“It does sound like a signal meant for us. Shall I flick through?”

“Not yet. Have you found anything?”

“I believe I’ve traced the lines of a tremendous hatch inside the waterfall. It would pass a war fleet or a patch to cover the crater in Fist-of-God. There may be signals to open it. I haven’t tried.”

“Don’t. Stand by. Hindmost?”

“I have radiation and deep-radar scans. The building is radiating little energy. Magnetic levitation does not require large amounts of power.”

“What’s inside?”

“Here.” The Hindmost gave them a view. By deep radar the structure showed translucent gray. It appeared to be a floating building modified for travel, with fuel tanks and an air-breathing motor built into the fifteenth floor. The puppeteer said, “Solid construction: walls of concrete or something equally dense. No vehicles in the carport. Those are telescopes or other sensor devices in the tower and the basement. I cannot tell if the structure is occupied.”

“That’s the problem, all right. I want to outline a strategy. You tell me how it sounds. One: we go as fast as possible to just above the peak.”

“Making perfect targets of ourselves.”

“We’re targets now.”

“Not from weapons inside Mons Olympus.”

“What the futz, we’re wearing a General Products hull. If nothing fires on us, we go to step two: we deep- radar the crater. If we find anything but a solid scrith floor we go to step three: vaporize that building. Can we do that? Fast?”

“Yes. We don’t have power storage to do it twice. What is step four?”

“Anything to get us inside quick. Chmeee stands by to rescue us any way he can. Now tell me whether you’re going to freeze up halfway through this procedure.”

“I wouldn’t dare.”

“Wait a bit.” It came to Louis that their native guests were scared spitless. To Harkabeeparolyn he said, “If there is a place in the world where the world can be saved, that place is below us. We think we’ve found the door. Someone else has found it too. We don’t know anything about him, or them. Understand?”

The woman said, “I’m frightened.”

“So am I. Can you keep the boy calm?”

“Can you keep me calm?” She laughed raggedly. “I’ll try.”

“Hindmost. Go.”

Needle leapt into the sky at twenty gravities, and rolled, and stopped upside down, almost alongside the floating building. Louis’s belly rolled too. Both City Builders shrieked. Kawaresksenjajok had a death grip on his arm.

Eyesight showed the crater plugged by old lava. Louis watched the deep-radar image.

It was there! A hole in the scrith, an inverted funnel leading up (down!) through the crater in Mons Olympus. It was far too small to pass Ringworld repair equipment. This was a mere escape hatch, but it was roomy enough for Needle.

“Fire,” Louis said.

The Hindmost had last used this beam as a spotlight. At close range it was devastating. The floating building became a streamer of incandescence with a cometlike head of boiling concrete. Then it was only dust cloud.

Louis said, “Dive.”

“Louis?”

“We’re a target here. We don’t have time. Dive. Twenty gravities. We’ll make our own door.”

The ocher landscape was a roof over their heads. Deep-radar showed a hole in the scrith, dropping to engulf them. But every other sense showed the solid lava crater in Mons Olympus descending at terrible speed to smash them.

Kawaresksenjajok’s nails in Louis’s arm were drawing blood. Harkabeeparolyn seemed frozen. Louis braced for the impact.

Darkness.

There was formless, milky light from the deep-radar screen. Something else was glowing somewhere: green and red and orange stars. Those were dials on the flight deck.

“Hindmost!”

No answer.

“Hindmost, give us some light! Use the spotlight! Let us see what’s threatening us!”

“What happened?” Harkabeeparolyn asked plaintively. Louis’s eyes were adjusting; he could see her sitting on the floor, hugging her knees.

Cabin lights came on. The Hindmost turned from the controls. He looked shrunken: half curled up already. “I can’t do this any more, Louis.”

“We can’t use the controls. You know that. Give us a spotlight so we can see out.”

The puppeteer touched controls. A white diffused light bathed the hull in front of the flight deck.

“We are embedded in something.” One head glanced down; the other said, “Lava. The outer hull is at seven hundred degrees. Lava was poured over us while we were in stasis and is now cooled.”

“Sounds like someone was ready for us. Are we still upside down?”

“Yes.”

“So we can’t accelerate up. Just down.”

“Yes.”

“Want to try it?”

“What are you asking? I want to start over from just before you burned out the hyperdrive motor—”

“Come on, now.”

“—or from just before I decided to kidnap a man and a kzin. That was probably a mistake.”

“We’re wasting time.”

“There is no place to radiate Needle’s excess heat. Using the thrusters would bring us an hour or two closer to the moment when we must go into stasis and await developments.”

“Hold off for a while, then. What are you getting from deep-radar?”

“Igneous rock in all directions, cracked with cooling. Let me expand the field… Louis? Scrith floor some six miles below us, below Needle’s roof. A much thinner scrith ceiling fourteen miles above.”

Louis was beginning to panic. “Chmeee, are you getting all this?”

He was answered in unexpected fashion.

He heard a howl of inhuman pain and rage as Chmeee burst from the stepping disc, running full out with his arms across his eyes. Harkabeeparolyn dove out of his path. The water bed caught the kzin across the knees