The next few minutes unspooled with growing panic, more and more rapidly, like a harpoon line in a speared sea monster diving deeper and deeper.

Niko said he’d never found any keys. And as I tried to piece together the evening, to backtrace what had happened, little details kept failing to add up. The vodka bottle. The movie quote: now he agreed with me, was baffled that I thought he could possibly get it wrong. He pulled out his phone and showed me the last text from his ex: four months ago.

Despite these discrepancies, something felt right about the way we discussed them. We were back in sync again. The strained awkwardness and stunted conversations of the last week were gone entirely. It felt like he’d been away on a trip and we were just now catching up again, despite the fact that we’d been seeing each other all week.

But when I told him where I’d been that night, about the fridge and the keys, it was like I’d punched him in the face.

He bolted up, took a few paces, then collapsed into a chair, stricken. “Oh, shit,” he kept saying. “Oh shit oh shit oh shit.”

He wouldn’t say anything else until I poured him another shot of vodka—the vodka we’d already finished, goddammit—and then the story started breaking out of him, in sharp-edged pieces.

“Remember the night of the party?” He looked drained. “I didn’t feel like talking, you know, to other humans. So I went exploring. Had a vague thought like maybe I’d find something interesting to bring back up and show you.” He ran a shaky hand through his kinked hair. “But something...” He swallowed. “Something happened, okay? And I got to the pool room and I couldn’t go back the same way.” He waved a hand at my raised eyebrow. “Let me just finish telling this, okay?”

He wouldn’t say what had happened, but it made him take a sudden diversion, and after wandering through unfamiliar halls for a few minutes he found himself approaching the pool room door from the other direction. He climbed the ladder into the kitchen, but when he got there he found the fridge not only unlocked, but open—the outer door, at least. He’d done the same thing I had: climbed inside, pulled the outer door shut, lost his light, pushed the other door open—and had climbed out with the same spatial confusion I’d had.

I told him my theory about knocking the fridge around, but he shook his head. “No, I don’t think so. When my light went out, I was pretty deliberate with my motions, exactly because I didn’t want to get turned around. I barely jostled the thing. And there’s something else that makes me think...”

He swallowed, licked his lips. For a long minute, he couldn’t meet my eye. Then he grabbed my knee, as if to steady himself, looked over at me. Looked hard. “Ryan. Man. This is going to sound crazy. But listen, okay? This place. This house.” He looked around furtively, as if we were someplace dangerous and not the living room of our college crash pad. As if it could hear us. “We’re not where we used to be. This is a different place.”

“Step off,” I said, rejecting this at once. “It’s one thing to say there’s a couple mirrored hallways down there, but there’s not an entirely different house up here. There aren’t clones of our goddamn roommates, a different street and sky and...”

I trailed off, because he was staring at me, miserable. I realized this was exactly what he thought was happening.

“Look,” I said, worried and afraid, “let’s go back right now. I’ll show you the coffee stain. That proves it. We can find the other key and—”

“I’m not going back down there.” He pulled back his hand abruptly. “I’ve been too damn terrified to even think about it, after what I...” He bit his lip, looked away. Took the last swig of vodka.

Tingles crawled down my neck. “What you saw? Well, what was it?”

He didn’t answer for a while. I thought he was trying to remember at first, and then maybe that he was trying to forget.

Finally, defeated, he told me. “On my way down. Before I got there. I started feeling... off. Like something was wrong.”

“That happened to me, too. I hid in a side room and waited, and after a while it just kind of went away.”

“Yeah,” he said weakly, “probably what I should have done. You know me, man. I ignored it. I kept going. And...”

He stopped, visibly shaking. Phantom insects crawled up my back. What did he see to rattle him this bad?

“That long hallway. Without any doors. I was walking down it, and I saw another light.”

I sat rigid. “What the fuck?”

“I kept walking,” he went on, not looking at me. “I didn’t want to turn my back, get chased down. That sick feeling got stronger. Sharper. But I couldn’t stop walking. Couldn’t turn around.”

He took a deep breath. “The light got closer. It was someone with a flashlight. They were coming towards me just like I was walking towards them. I couldn’t see their face. I just kept walking. I kind of hugged the right wall and they hugged the left. The flashlight was right in my face. I couldn’t see anything until we were only a few steps apart.”

He finally looked up at me, forehead wet with cold sweat, like he was reliving that queasy sensation. My own stomach twisted. I couldn’t breathe.

“Ry,” he said, “I passed myself. I walked right past another me with another flashlight, who looked as sick and fucked up as I did. And we both just kept walking. We didn’t stop. I made it to the pool room, climbed the ladder, and went right through that fucking fridge to get farther away. And there is no fucking way I’m going back down there again.”

I swallowed. “Dude. It was dark. You were messed up. Maybe you saw someone else down there, but what you’re saying, man. It’s impossible.”

“Irrational.” He laughed hollowly. “Things are different here. On this side. I’ll show you. What’s the smallest bill you’ve got in your wallet?”

“Uh, I don’t know.” Taken aback, I pulled out my wallet, riffled through the smaller bills. He smiled grimly at one of them, snatched it, held it up.

“Better hold onto this. Because no one here’s ever heard of one.”

“What are you talking about?” I said, annoyed.

And over the next hour, he showed me.

We pored through the dusty encyclopedia in our front foyer. We combed the magazines sitting in the house, dragged out Monopoly. We fired up the Internet (all Geocities and tedium in those days) and found pictures of cash registers, government websites, coin collectors talking about the history of currency.

According to everything we could find, the US Government had never, at any point in its history, issued a three dollar bill as legal tender.

We stared at the one from my wallet with growing unease. Buchanan’s familiar portrait stared back, implacable. Niko tapped the portrait’s chin. “That right there might be the only one that exists in this place. Wherever we are.”

We cobbled together a theory out of guesswork and dreams.

If Downstairs had two sides—two versions, or halves, or whatever—then Niko had passed into the other one that night of the party, through the unlocked fridge. The Niko I saw stumbling out of the hall that night, sick and wanting sleep, was the wrong Niko. A different Niko. The one my Niko had passed in the hall.

And that Niko didn’t quite fit in. Everything was a little off about him, and from his perspective, I suppose, about me.

But that Niko had found two keys. We had no idea where he’d found them. But if he’d passed through the fridge with one of them—and here I will compress the part where we opened another bottle of vodka rather than accept the ridiculousness of this garbage fairy tale premise where a magical Frigidaire is a gateway between worlds, slept it off, suffered through ugly hangovers the next day, and finally reconvened late in the afternoon with some Aspirin—if the other Niko came through the fridge just before my Niko had, that could explain why my Niko had found it unlocked and open, was able to pass through.

And earlier—if we followed this chain of logic—I’d been drinking from a different vodka bottle, in a different house, with that other Niko. The one with the keys.

I’d stolen them and passed through to this side of Downstairs—the wrong side—and maybe some other me had been doing the same thing. I only avoided him by my sudden detour, when I sensed something wrong up ahead and ducked into the side room with the sheet-covered furniture, to let him pass by. And now we were both in the wrong house, on the opposite side from where we’d started.

“And both of them are on the wrong side, too,” Niko said, still wincing from the hangover.

I licked my lips, head also still spinning, wondering if it would be okay to take two more Aspirin. Or four more. “But these other two, if they exist.” I still couldn’t quite surrender to this madness. “The other two now have both the keys, right?”

Niko frowned. “What do you mean?”

“I left one in the fridge on the other side—our original side—when I went down last night. And the other, the bent one, on the counter. Also on that side. They’re both on that side.”

His face soured. “And the door locked behind you. So there’s no way for us to get back.”

“Unless there are two keys on this side too.”

“No. You said the first one you tried didn’t work, even though it looked the same? I think there’s exactly two keys. One for each side. The other me ended up with both, somehow. I guess if he found one and went through, he’d know right where to look for the second.” He took a breath, let it out. “So yeah, you’re right. They’ve got both keys. Unless they come back through, we’re stuck here.”

We stared at each other.

“What does that mean?” I finally asked.

“I have no fucking idea. But shit, man, I’m glad you’re here.” He ran a hand through his curls, face pale. “I seriously wasn’t handling this on my own. This whole last week, things weren’t right. You weren’t right, and I couldn’t stand that, man. I was going crazy without you. Doubting everything, you know how I get. Doubting who I even was. But this, this is...” He waved his hand back and forth between the two of us, then knocked it on the table. “You get me. We’re tight. Yeah? In it together, I mean. It’s good. I’m glad.”

I didn’t say anything, but I didn’t have to. I felt the same way and he knew it.

I slept in his room that night, in a sleeping bag beside his bed. He didn’t want to be alone. I’d kind of wanted some time to process everything but I didn’t protest too much. I liked being his anchor. He kept us both up late talking about random bullshit, rambling. It was okay. Everything was upside down. Old comforts couldn’t hurt.

We slept in the next day. Call me a coward, but buried in my sleeping bag I could pretend I wasn’t in the wrong universe.

Things were definitely wrong. Now that I was looking, I couldn’t deny it. Familiar people acted strange in a way you couldn’t put your finger on. Colors seemed indefinably different shades. A vague sense of off-ness suffused everything, like a movie with the sound a frame out of sync.

After looking more closely, things were off about my room. There was an unfamiliar dress shirt on a hanger. My copy of Samuel Delany’s Dhalgren was missing, along with all the other books of his I’d discovered after reading that one. It wasn’t quite my room, I realized. It was someone else’s.

It was mostly little things, so we grasped at each quantitative difference, each change we could pin down. One night one of our housemates kept saying something I didn’t understand. She was going on about getting a parking ticket and kept saying it was the “fourth fucking time” it had happened.

“What’s that word you’re saying?”

“Fucking,” she clarified, unhelpfully.

“No,” I said. “Count up in ordinals. You know first, second...”

She blinked at me. “First, second, third, fourth, fifth.”

Fourth. Instead of fourd.

Things were different here.

We didn’t find too many obvious changes. I was pretty sure the vice president had a different middle name, though I wouldn’t have staked my life on it. Postage stamps cost 35 cents instead of 33. Usually we weren’t quite sure whether something had actually changed, or we were losing our goddamn minds.

We danced around it for a while, but finally the phrase came out: parallel universes. But it didn’t really satisfy. Why these two universes in particular, out of a supposedly infinite number? Why were they connected via a series of poorly decorated basement rooms and linked together by a refrigerator, of all things?

At one point, feeling overwhelmed, I called home—not to tell mom what was happening because I didn’t want her to freak, just to hear her voice—but the answering machine said they were on vacation till the end of the month. This was doubly annoying, both because I hadn’t heard about any long vacation, and because “we” presumably meant her and my sister, and for some reason I hadn’t been invited, which made me feel even more out of place and abandoned. I was three hours away, not on a different planet.

Feeling rejected, I went record shopping, ill-advisedly adding a couple hundred dollars to my already terrifying credit card debt in exchange for a small stack of LPs. Lately I’d gotten obsessed with sci-fi audio book recordings. I found a few treasures at my usual haunts: Leonard Nimoy reading Ray Bradbury, and a six-record set of one of the Dune novels, read by Frank Herbert himself, still shrink-wrapped. More and more I only bought stuff in its original wrapping, unopened, sleeves protected from scuffs and wear marks, the records inside unplayed and undamaged, which is how I’d keep them.

Dad was the one who got me into records, back when I was still a kid and he was the most amazing person in the world. He took me to Disneyland, just the two of us (I don’t remember now why mom and my sister weren’t there), and we stayed late to see the Main Street Electrical Parade, and on our way out, way past my bedtime, he got me the record, my first record. I have eight different versions of that album now, six still in their original shrink-wrap. That first one I played so much it got scratched beyond belief, had to be constantly nudged forward out of stuck grooves, the cardboard sleeve beat to hell and back. I’ve still got that one, too.

I’d idolized dad. He’d worked for the Department of Agriculture, which doesn’t sound that glamorous but was legendary in my mind: my understanding of his job was that he traveled around the country helping farmers grow food better, the food that everyone in the country ate, and to me that was as noble and heroic as being an astronaut. Because of his job we had to move every couple years, and so I never really had any long term friends. Except him. My sister and I were never that close—even as kids, our interests were too different—but dad and I, we understood each other. We were always there for each other.

Maybe it was because of what happened with dad that I got so needy with my friendships later on, desperate to hold on to them. I either wanted to be your best friend in the world or not interact with you at all. That wasn’t really a recipe for a healthy social life in high school. I had a few friendships, here and there, but they didn’t last: I’d cling too hard and people would drift away. Niko, I guess, was the first one who ever clung back.

Thank God I had him back again.

We stayed close, maybe inevitably now that we were the only matching pair in this entire universe. It felt easy to be closer to him, for us both to need each other. It felt right. A relief from the wrongness all around us.

He thought my airlock idea had legs. Downstairs was made from house-stuff: hallways and empty rooms and appliances. A fridge was one of the few devices in that context that could maintain a seal. It was a cute concept except it didn’t actually explain anything.

It took a long time to convince him we needed to go back down.

“Maybe we can just stay here, and they can stay there,” he said. “So everything’s off a little. So what? It felt way more wrong to get close to...” He waved a hand. “Him. Whoever. My handsome twin. So maybe we should leave well enough alone. Brick the fucker up and never look back.”

Then the headaches started.

They were odd headaches. Not severe. A tinge of nausea and dizziness, like stepping off one of those fairground rides that whirls you around, and only a very distant pain. They came and went. But I took them as an ominous sign.

Niko said he’d been getting them all week. Oh. And they’d been getting stronger.

So the headaches more than anything convinced us. We had to go back down, at least try to figure out what was going on, or at least how we could get back. Maybe the fridge wasn’t the only connection. Maybe there were other keys, other doors. We’d barely started exploring. There was so much left.

But first we had to solve what Niko called the Mere Paradox.