I wanted to find my Niko, but this strange alternate argued against it. Impossible, he said. Like finding a needle in a haystack. Except this haystack went down forever. In the best-case scenario, he explained patiently, we’d wander until our food ran out, and then with our last dregs of energy and luck find our way back up to the surface and out, empty-handed.

He didn’t mention the worst-case scenario.

We argued. He insisted the smartest strategy was for us to retrace my steps to the base of the slide and find a way to climb back up. “The closer to the top, the fewer possibilities,” he said, “the fewer choices. And fewer chances of making the wrong one.” When he found out I hadn’t actually seen my Niko since we got separated in the shaft, he grew even more convinced. “Maybe he’s not down here at all. Maybe he caught himself on the way down, like you said, and he’s up there now waiting for you. Worrying.” He gave up convincing me. “Or if he’s not, he’ll realize heading back is the smart option. I know he would, buddy.” He tapped his head. “Trust me.”

I couldn’t deny this plan made sense, but I felt sick. Too much was wrong. “Look. Even if I take you back up there, it won’t be your world. You can’t stay. If you’re on the wrong side too long, you start to feel—detached.” I shuddered without meaning to. “Like it’s rejecting you. Like antibodies swarming. It’ll kill you.”

He shrugged. “You don’t know that. I’ll risk it. Anything’s better than staying down here.”

“It’s not just that,” I said, feeling like a coward, but I desperately wanted an excuse, a reason he couldn’t come back with us. “You know about that sick feeling when you’re too close to a twin. That’s even worse than the headaches. So say we find my Niko and get you both back to the surface. Then what? The two of you get a double on campus, move in together?”

“No.” He sighed, impatient. “You think I haven’t thought this through, all the time I’ve had? You help me get back up, I’m gone. It’s a big planet. I’ve learned how to survive. I’ll never get within a hundred miles of either of you again.”

“Wait a minute.” I’d had an idea. “That sick sensation, when you’re too close. We can use that to find him.” He raised an eyebrow. “Okay, maybe you’re right, and there’s too much space here to find him by dumb luck. But you’ve got a sixth sense for where he is. You’re like a magnet we can move through that haystack, feeling for tugs. Any twinges and we steer closer, till we’re close enough to do the rest by shouting.”

“You’re not listening to me, Orion.” He was getting angry. He realized it, took a moment to collect himself. “There’s a lot of space down here,” he went on, more reasonably. “You have no idea how much space. You’re never going to find him. You need to accept that. You’ll get us both lost. And I’m sick of being lost, buddy. Fucking sick of it.”

He had an intensity my Niko never had—though maybe there’d been something like it latent in him, waiting for the right trauma to pull it out like a loose thread. It scared me.

He was right. I didn’t want to get lost down here, either. I didn’t want to end up like him.

But I also wasn’t willing to give up on my Niko.

I dug out my keys, held them up. “Look. I’ve been using these to mark my way. There’s no chance of getting lost. And I’ve got plenty of food, still. For both of us. So we keep searching. Keep marking the way. Be methodical, map it out. And if the food runs low...” My throat felt tight. “If that happens, we’ll turn back. But I can’t give up on him yet. I can’t.”

His eyes narrowed, and I could see him weighing something behind them.

But then his face relaxed. A huge smile broke across it, and it was so familiar, so him, that when he threw his arms around me and squeezed me tight, I hugged him back.

“Goddammit, man, you haven’t changed at all. Okay.” He pulled back, still grinning, and laughed—a real laugh, the one I remembered. “Shit. Like you’d give me up without a fight. Course not. The fuck we waiting for, then?”

He hoisted his pack, started down the hall. “Come on, man,” he shouted back over his shoulder, “let’s go find me.”

Elder Niko was obsessive about marking our way—I couldn’t blame him—so we made slow progress. But despite his initial misgivings he seemed completely committed to finding his younger double now. Even downright cheerful about it.

We slipped into something like a rhythm, despite the surreal circumstances. He borrowed a glowstick—the penlight or whatever in his shirt pocket must have been dead—and kept up conversation as he swung it around, peering down all the hallways we passed. Sometimes, for a moment, I’d forget it wasn’t him. Then the light would catch the hard-edged crow’s feet around his eyes, or he’d ask in nostalgia-tinged tones if I remembered something that happened a week or a month ago, and reality crashed back into me. I supposed from his perspective I was like a long-lost friend at a high school reunion, so as woozy as it made me feel I could understand this behavior.

I thought I could, anyway.

The sense that he was keeping something from me, that something was wrong, only grew. He kept asking about the way back up: casually, like making conversation. But he wanted to know what was above the slide, the layout of the rooms before that, which branch I’d taken off the Big Room to get down here. He was trying to reconstruct the route back out. Maybe this made sense—maybe he was just curious, or hedging his bets in case we got split up, like I had with my Niko—but behind the jokes and easy laughter I sensed calculation. A front. And I had no idea what could be behind it.

Now and then I’d ask if he’d gotten any twinges of feeling, hints we were getting close to another Niko. He’d answer right away: Nope. Nothing. Sorry. At one point, annoyed, I demanded he stop for a minute and really try. He put on a show of being abashed, of closing his eyes and concentrating—but I could tell it was only an act. He wasn’t expecting to find anyone.

Like he knew there was no one to find.

We’d come to a place of endless ducts and exposed plumbing. Bulky metal curves and protrusions poked from the walls: the bones of water heaters, of central air. The ground was dry, but the room felt hot and moist, dripping all around us. We poked around a space the size of a mansion, cluttered with oddly-sized corners and crannies, finally realizing the whole area was a dead end. There was no other way out.

“Maybe it’s time to turn back,” Elder Niko said solemnly when we realized this. We were near the back of the big cluttered space. A smell like rotting leaves wafted from the sharp metal ruins of a boiler that looked like it had ruptured from the inside. The carpet was mottled with rusty blotches, like overlapping pools of dried-up blood. “Man, it’s going to be hilarious when we find out my younger self’s been topside this whole time. Lounging on a blanket in the backyard, you know, under the sky. Catching some rays. Listening to tunes. Waiting for you to get out.” He laughed, and his voice echoed strangely off a thousand metal boxes.

His face grew more serious. “Or maybe he’s so lost we’ll never find him. Orion. I tried to tell you. This place is too big.” He gestured around us, took a deep breath, looked chagrined. “It’s a lost cause, buddy. I think it’s time to give it up.”

He took a step back toward the door, but I was in his way, bristling. Holding my ground.

He stopped, looking confused. “What’s up?”

I couldn’t explain my trembling, except for a deep-seated certainty that this was wrong. Everything about it was wrong, just generally, but a specific wrong thing was the way this place had taken Niko from me and done this to him, made him into something I couldn’t understand and didn’t trust, and suddenly it was too much for me. Some yawning possibility loomed before me, like I was blindfolded on a precipice, about to step forward. But I had to know. Better to fall than keeping lingering on the edge.

I met his eyes. “Tell me.”

“Hmm?”

“Tell me whatever you’re not telling me. Tell me what’s really going on. I want to know.”

He frowned. “What do you mean?”

“Damn it, stop pretending. Everything is not okay. You’re stringing me along and you need to stop it. Be honest with me.”

“Oh?” His expression had started to shift. Something was slipping.

“Stop playing games.” I clenched my fists. “Stop using me. Look, we can do this together. You need me to get out of here. Both of you do. I know the way back, and I’ll help you, but I need to trust you. And you need to trust me. Okay?”

He nodded, looking serious, and bowed his head. Then gave himself one final nod. As if coming to a decision.

He looked up smiling, stepped forward, and punched me in the throat.