“Yes.”

“Jones, you amaze me.”

“What’s more, number three is right near the center of that big excavation that Brinston and his folks found. That’s interesting. For the longest time I’ve thought that it was the triangular liths that our attention was being drawn to. Now I’m pretty sure it’s this one — that it’s the center of the henge.”

“But why?”

“I don’t know.”

“You don’t know!”

“No! Perhaps to satisfy an alien geometry, perhaps to provide a key to a code — it could be anything. My brilliant investigation has gone only so far.”

“Ho, ho.” We circled the lith slowly, looking for some remarkable sign, some new attribute. There were none evident. A rectangular slab of ice-

A thought, slipping at the edges of consciousness. I stopped and tried to retrace my thinking. Stars, nothing… I shifted my head through the position it had been in when I had the thought, tried all the other remembering tricks I knew. I looked up at the top of the lith, and stepped back, and as I did so a bright star appeared, defining the top of the lith. Was that Kachab, brightest star in Ursa Minor? I found the other stars of the constellation — it was. Pluto’s Pole Star.

I remembered. “Inside it,” I said, and heard Jones’s surprised breath. “That’s it! There’s something inside it.”

Jones faced me. “Do you really think so?”

“I’m certain of it.”

“How?”

“Holmes told me. Or rather, Holmes gave it away.” I reminded him of the model with the laser sight lines, in the spherical planetarium: “And there was one beam of blue light pointing straight out of the tallest lith. It must have been this one. And it was the only laser beam coming directly out of a lith.”

“That could be what it means, I suppose. But how do we find out?”

“Listen,” I said. I pressed my faceplate against the surface of the lith and rapped hard on the ice. A certain vibration… I hurried to the adjacent lith and did the same. Vibrations again, but I couldn’t tell if they were different.

“Hmm,” I said.

“I hope you wouldn’t melt holes in it—”

“No, no.” The certainty of my guess, which had felt so much like an act of memory, didn’t fade. I switched my intercom to a landing vehicle band. “Could you get me Dr. Lhotse, please?” The crew member called him up.

“Dr. Lhotse? This is Doya. Listen, could you run an easy test to find out if one of the liths had any hollow spaces in it?”

“Or spaces occupied by something other than ice?” Jones was on the band as well.

Lhotse considered it for a moment — it sounded as if he had been asleep — and then supposed that some mass tests, or sonar and x-ray and such, could determine it.

“That’s excellent,” I said. “Could you bring out the necessary gear and people?… Yes, now; Jones and I have found the key lith and we suspect there is a hollow in it.” Jones laughed aloud. I could imagine Lhotse’s thoughts — the two strange ones had finally gone over the rim…

“Is this serious?” Lhotse asked. Jones laughed.

“Oh, yes,” I said. “Quite serious.”

Lhotse agreed to do it and hung up. Jones said. “You’d better be right, or we may have to walk home.”

“There’ll be something,” I said, feeling an apprehension that verged, curiously enough, on exhilaration.

“I hope so. It’s a long walk.”

There was a hollow column in the center of the lith, running from top to bottom.

“I’ll be damned,” said Lhotse. Jones and the sonar people were whooping. Searchlights flashed off the ice as from the surface of a mirror. Circles and ellipses of white bobbed around the ground and caught dancing figures, flashed in my eyes. The surrounding scene was blacker, more obscure. My heart pounded the inside of my chest like a living child.

“There must be an entrance at the top!”

There was an extension ladder that could be roped to the liths, on the other side of the site. Lhotse ordered the people he had brought with him to set it up, and he called back to the LVs. “You’d better get out here,” he told Brinston and Hood and the rest. “Jones and Doya found a hollow lith.”

Jones and I grinned at each other. While they were moving the ladder across the dark old crater bed, Jones told Lhotse the story of our search. I could see Lhotse shaking his head. Then the ladder was moored against the lith and secured. Huge lamps, their beams invisible in the vacuum, made Lith number three a blazing white tower, and it cast a faint illumination over the rest of the henge, bringing the beams into ghostly presence. Lhotse climbed the ladder and set the next section in place. It just reached the top. I followed him up, and Jones clambered at my heels.

Lhotse kneeled on the top, roped himself to the ladder securely. I looked down; the painfully bright lamps seemed far below. Lhotse’s quiet voice in my ear “There are cracks.” He looked up at me as my head rose over the edge, and I could see that his face was flushed red, and dripping with sweat. I myself felt chills, as if we were in a wind.

“There’s a block of ice here plugging the shaft. It’s flush with the surface, I don’t know how we’ll get it out.” He ordered another ladder sent up. There were a lot of people talking on the common bands, though I couldn’t see many of them. I tied myself to the ladder and climbed onto the top of the lith. Jones followed me up. It was a big flat rectangle, but I worried that it might be slippery.

Eventually we secured a pulley above the lith, on two ladder extensions, and then sank heated curved rods into the plug. The line was rigged and when those on the ground pulled, the trap door — a square block about three meters by three by two, cut like a wedge so it would fit into the top snugly — rose up easily. The blocks of ice were too cold to stick to each other. Jones and Lhotse and I, standing on the ladders, stuck our heads over the black hole and looked down. The shaft was cylindrical, and a little smaller than the plug cut. With a powerful light we could distinguish an end or turning in the shaft, far below.

“Bring up some more rope,” ordered Lhotse. “Something we can use for belay swings, and some of those expanding trench rods. If we used crampons we’d kick the lith down before we cut even a scratch in this stuff.” The block was lowered, the ropes brought up, and we were tied into torso slings, and given lamps. Lhotse climbed in and said, “Let me down slowly.” I followed him in, breathing rapidly. Jones hung above me like a spider.

The walls of the shaft were slick-looking under our bright lights. We inspected the ice as we pushed off and descended, pushed off and descended.

Lhotse looked up. “You probably should wait till I get to the bottom.” The people at the top of the ladder heard him and Jones and I slowed. Lhotse dropped away swiftly.

The descent lasted a long time. Our lamps made the ice around us gleam, but above and below us it was black. The ice changed to dark, smoothly cut rock. We were underground.

Finally we hit a gravelly floor. Lhotse was waiting, crouched in the end of a tunnel that — I struggled to keep oriented — extended away from the ring, therefore northward. It descended at a slight slope. Ahead lay pitch blackness.

“Send another person down to this point for a radio relay,” said Lhotse, and then, holding his lamp ahead of him, he hurried down the tunnel.

Jones and I stayed close behind him. We walked for a long time, down the bottom of a cylindrical tunnel. Except for the fact that the walls were rock-solid basalt, the tunnel had been bored through it — it might have been a sewer pipe. I was shivering uncontrollably, colder than ever. Jones kept stumbling over me, ducking his head at imaginary low points.

Lhotse stopped. Looking past him I could see a blue glow. I rounded him and ran.

Suddenly the tunnel opened up, and I was in a chamber, a blue chamber. A cobalt blue chamber! It was an ovoid, like the inside of a chicken’s egg, about ten meters high and seven across. As Lhotse’s lamp swung unnoticed in his hand, streaks and points of red light gleamed from within the surface of the blue walls. It was like a blue glass, or a ceramic glaze. I reached out and ran a gloved hand over it; it was a glassy but lumpy surface. The points and lines of dark red came from chips under the surface… Lhotse raised his lamp to head level and rotated slowly, looking up at the curved ceiling of the chamber. His voice barely stimulated the intercom. “What is this…”