That made her mind up for her and she found that she could jump it, and with very little effort, either.

But I’ll have to admit that old-collecting-chute-hand or not, I wasn’t prepared for what we found next. In the darkness, there was no floor in front of us. Above us, no ceiling. My light showed our own corridor resuming on the far side of the gap, fully six feet away. The floor sloped sharply down and the air rushed strongly along. I had never encountered an up-anddown duct of this size before.

“Well, what is it?” Zena asked.

There were handholds at the side on which to cross the gap, and holding onto one of these, I leaned over and dropped a piece of broken chalk in a futile attempt to gauge the depth of the cross-duct. I listened, but I never heard a sound.

“It must connect one level with the next,” I said. “A main line. I bet it goes straight down to the First LeveL”

“Well, don’t you know?”

“No, I don’t,” I said. “I’ve never been here before.”

I wasn’t about to jump that distance, so I examined the hand- and footholds carefully. If you slipped and fell, and it was as far down as I suspected, all that would be left of you would be jam. I shone my light up and down, and the beam only managed to nibble at the blackness. The holds went up-and-down, too, as well as across, a ladder that went much farther than I could see.

“Maybe it connects with the Fourth Level down there,” Zena said, “but where does it go to up there?” She pointed straight up the duct.

I didn’t know. The Fifth Level was the very last, the outside, but this duct went beyond the Fifth. Air chutes don’t lead into blind corners and air doesn’t come from nowhere.

“I don’t know,” I said. “But as long as we’re here, why don’t we see where it goes?”

I reached over and put my toe in the inset in the wall. Then I grabbed the first handhold I could reach and swung out. They were good finn holds and while the distance straight down bothered me a little, as long as I couldn’t see how far down it was I wasn’t really scared. I once had the experience of walking along a board three inches wide while it was set on the ground — I went the whole length and probably could have walked on for a mile and never fallen off. Then the board was raised into the air and I was challenged to try again. When it was set on posts ten feet high, I wouldn’t even try it because I knew I couldn’t make it. This was something of a similar situation, and as long as I couldn’t see I knew I wouldn’t worry.

I grabbed the next hold and started up. Before I could get anywhere, Zena leaned over and held me by the foot. “Hey, wait up,” she said, and gave my foot a tug.

“Watch it!” I said sharply. “You’ll make me fall.” I tried to jerk my foot loose, but she wouldn’t let go.

“Come on back down,” Zena pleaded.

Reluctantly I came down. I said, “What is it?”

“You can’t go and just leave me.”

“I’m not leaving you,” I said. “Just follow me and you can’t be left behind.”

“But I’m scared,” she said.

That was really the time for her to finally admit it. We had both known that from the beginning, but she had refused to admit it until things were getting interesting.

“It’s not going to hurt you,” I said. “All we have to do is climb until we find out what’s up there.” I could see she was wavering, caught between the fear of climbing the ladder and the fear of being left behind. “Come on,” I said. “You first.” I wanted her to go first. That way she couldn’t grab me again.

After a moment, I edged her down the beginning of the slope to the first handhold. I got her onto the ladder and actually moving again. I followed her. I had the light clipped at my waist, pointing upward and giving both of us some’ idea of what and where to grab as we continued to climb.

I could hear Zena whimpering as she climbed, making scared noises in her throat. To get her mind off her troubles, I said, “Can you see anything up there?”

She was clinging tightly to the ladder as we went up, and now she stopped, flipped her head up for just the shortest instant and then brought it down again.

“No,” she said. “Nothing.”

I should have known better, I told myself as we continued to climb. You don’t bring somebody who has a habit of choking up into a situation like this.

Suddenly, without any warning, Zena stopped moving. Before I could help myself, my head rammed so hard into her foot that a shock of pain ran through my neck. If I’d had my head up, I would have seen that she’d stopped, but you can’t climb indefinitely with your head thrown back without getting a crick in your neck. I stopped immediately and went down one step.

“What’s the matter?” I asked.

“I just can’t go any farther. I can’t.”

I lifted my head and peered upward. I couldn’t see anything beyond Zena that would hold her up. She was just clinging to the ladder, her face pressed close to the metal. I could hear her breath rasp in her throat.

“Did you run into something?”

“No. I just can’t go any farther,” she said tearfully. “I’m scared.”

I reached up and put my hand on her leg. It was rock-hard and trembling. I said, “Move ahead, Zena,” in a firm but gentle tone — I didn’t want to frighten her — and pushed at the calf of her leg, but she didn’t move.

I could see that it had been a mistake to be in the lower position on the ladder. If Zena let go and fell, I would be swept along no matter how hard I tried to hold on. That would save me trying to explain what had happened — and it might be difficult to explain if I came back by myself without Zena: “Oh, she fell down one of the air chutes” — but that wasn’t anything to be happy about. I was genuinely frightened. My heart was beginning to speed up and I could feel a trickle of sweat running down my back.

“Don’t let go, Zena,” I said carefully.

“I won’t,” she said. “I won’t move.”

I unclipped the light at my belt and then I leaned back as far as I could until I could see beyond her. It would take twenty minutes to go down the ladder — in her state, probably longer — and even if I could start her moving, I doubted she could hold on that long. I held the light up at arm’s length over my head. About forty or fifty feet above us I could see something black at the side of the duct. A cross-corridor, perhaps, but I couldn’t be sure. All I could do was hope that it was.

“I want to go down,” Zena said.

We couldn’t go down. We certainly couldn’t stay where we were. I didn’t know what was ahead of us, but it was the only direction in which we could go.

“You’re going to have to climb a little more,” I said.

“But I’m scared,” Zena said. “I’m going to fall.”

I could feel sweat on my forehead now. A runnelet ran down and caught in my eyebrow. I wiped my brow.

“No, you’re not going to fall,” I said confidently. “I just looked up above, Zena, and there’s a cross-corridor just thirty feet or so over your head. That’s all you have to climb. You can do that.”

Zena just screwed her face in against the metal even harder. “I can’t.”

“Yes, you can. I’ll help you. Keep your eyes closed. That’s right. Now, move your foot up one step. Just one step.” I pushed at her leg. “That’s right. One step. All right, now reach your hand up — no, keep your eyes closed. Now move your other foot.”

One foot, one hand at a time, I got her moving again. For the first time since I could remember, the darkness seemed oppressive, a place where anything could happen. It was the way it must have seemed to Zena all along.

In a minute, I said, “It’s not more than twenty feet or so now,” but Zena was blocking my view and I couldn’t do anything but hope I was right. “You’re doing fine. It’s only a little bit farther.”

I continued to urge her on, and she went up slowly, a rung at a time. It was more than twenty feet, but not too much more than that, when Zena gave a little cry and was suddenly no longer above me. I looked up, and in the beam of the light clipped at my waist I could see the cross-corridor just over my head.