With my back turned to the fire, the dark maw of the tunnel is the only sight to greet me. I still prefer it to Sean's prying eyes. This is our third night trekking through the tunnels, and he has yet to say anything beyond the minimum. For days, the only noises have been shuffling feet, breathy exhales, and crackling flames. Even when I dropped the mushrooms into his lap, he didn't thank me. Then again, I shouldn't expect him to. Sean Rahkifellar is not a thank-you kind of man. He is clipped words, to-the-point sentences, and functionality over feeling. So that's what he'll get in return.

I wonder if he's still staring at me as I lie here. While we ate, I watched the fluid patterns the fire painted on the wall, and he watched me. It's a habit he had in the lab as well, like he was trying to peel back my skin and read the meaning hidden in the tension of my muscles. To him, I am but a specimen on a dissection tray.

I never let him know it bothers me, though. Instead, I always just slide my eyes to meet his, and he flicks his gaze away, knowing he's been caught.

Pulling my blanket tighter, my cold fingers trail up to my necklace. The metal provides no warmth, but as I pull it out, a wavering smile tugs at my lips.

The charm dangles from a tarnished silver chain. The pendant itself, though, shines as if new, glittering with a sheen like clear oil on glass. It's sculpted to mimic an old-timey shield, the kind depicted in children's fairy tales where brave warriors march into battle. Embossed in the center, a sparrow flies against the moon.

It'll protect you, my dad said when he drew the necklace out of its dusty, padded case. And as long as you're away from home, it'll remind you where you come from.

Knowing I was only going to be studying topside for a few months, I joked it off, but I was touched, and I ached to put the heirloom on. Its obvious age somehow enhanced its beauty and air of mystery.

But that was back when my only goals were earning my masterate in vitaliti, the study of living things, and getting an official, paying research job in Erreliah. The only step that still stood between me and that was a stint of field work above ground and a dissertation. At least, that's what I thought.

I slip the necklace back underneath my shirt, looking forward to sleep. Somehow, dreaming feels louder than the restrained hush does.

In the morning, the silent dance between me and Sean continues. We prepare for the day's hike, moving around each other without intersecting, observing without being observed, the empty communication between us almost more tangible than real conversation.

Sean's collapsible lantern is the only light source as we shuffle onward. Somehow, in my whirlwind of preparations, I forgot to bring light. Perhaps it's because for my entire life, it's been provided for me. In Erreliah, light twinkles from a thousand windows and lamps shine on every street, making it feel like the glow emanates straight from the city's core. Most people have something that glows on their person—a timepiece backed with moss, a miniature lantern on a necklace, transparent shoes whose gears churn and spark as they walk. At the very least, I could always rely on the moss planted liberally throughout the city and its well-traveled tunnels. The small plant may not provide much light, but it's better than the endless layers of midnight curtains hovering in this small, low-traffic path.

Since Karsix's Lesser West Tunnel doesn't connect to any other underground cities, its sole travelers are only ever the occasional poor topside merchant and undercity criminal. The disuse shows. Here, the only light is natural, sporadic glow-moss clinging to the high ceiling like faint stars on a cloudy night topside.

Ahead, our tunnel splits in two.

I glance around. "Where are the guide signs?"

Sean keeps walking. "You do realize that there are upwards of nine-hundred known underground routes in the High Valleys? Not all of them get signage. Especially the ones that lead out. Topsiders are the ones that put any effort into connecting below- and above-ground trade anymore."

"What, are you a cartographer now?"

"No," he calls back. "I paid attention in my geography classes."

Not bothering to consult me, he strides right up to the left tunnel, steps quick and confident and—

Hesitates.

It's just an instant, a falter in his steps, a quick look at the other path. Then his lantern lifts higher, and he continues forward.

I catch up. "Hold on!"

He doesn't.

I grab the sleeve of his coat and yank. He spins around. "What?"

Deliberately, I ask, "How do you know that this is the right tunnel?" He's half a head taller than me, but I look him straight in the eyes.

His gaze breaks, flicking to the dark behind us, but his words affect nonchalance. "Because, unlike you it seems, I prepare before departing civilization. There are these things called maps, you know." Now he meets my eyes. "You can study them for free in any local library. It's the left tunnel."

"Where is that going to take us?"

"A little trading post. Good enough to restock rations and get directions. Now, are you done interrogating me?"

He starts to turn, but I catch his arm. "Are you sure about this, Sean?"

"Yes, I'm sure! What good does asking me about it do anyway? I say it's the left tunnel. You don't have any better intel. That closes the matter."

"If we get lost—"

"Skies, Riveirre, we're not going to get lost! If it makes you feel better, this tunnel is inclining. See?" He gestures with the lantern. "Aside from anything else, that means it's heading topside. Alright?"

He heads off. Since he has the only light, I'm forced to keep up. Unease flutters in my stomach, though. Just because the tunnel is going up right now doesn't mean it won't dead end. Mr. Paid-Attention-in-Geography should know that. He almost certainly does know that.

A burst of nervous energy tingles in my veins. He doesn't remember, I realize. He doesn't remember which way leads to the post, or at least he isn't certain. I'd bet the last cent stone-mark in my pocket on it.

"Sean."

His steps snap crisply against the stone. "What?"

"Why don't we pull out the map and double-check? Just to be sure."

He pulls short, turns, and cocks his head. Slowly, he says, "I told you. The map is in the library."

I close my eyes, trying to process. "You're saying you didn't bring the map you found? Weren't you lecturing me on being prepared two minutes ago?"

"You mean I didn't steal the map I found? Yeah. That's what I said." He reaches into a pocket, popping the lid on a timepiece, and scrutinizes it as he responds. "I may be many things, Riveirre, but a thief is not one of them. Although I'm curious about you now." He clicks the piece closed and continues down the tunnel.

Yet again, I follow.

A few hours of silence later, Sean shatters the air. "We'll stop here."

He's pointing to a five-foot wide opening in the rock. Beyond, a path curves, the vague edges of a chamber entrance visible at its end. Lit by the warm, dull orange of the lantern, the scene looks more like a faded oil painting than crisp reality.

It isn't even quite lunch yet. "Why?"

He turns around slowly, as if I'm not worth the effort it takes to address promptly. The lantern swings with the motion, sending the shadows skittering across the walls. "Because," he draws out, "personally, I don't feel like killing the known world today. It's contrary to your opinions of me, I know," he says, holding up his free hand. "But for some reason, mass homicide wasn't on my to-do list this week." His eyes darken, serious now. He turns back and starts through the side-tunnel.

"You can't seriously be planning to quarantine here," I call. "It's only—"

"Four days out from Karsix? Yeah." He draws the word out, as if I'm a simple child. "And we're getting close to being topside. Haven't you been checking your barometer?" He smirks at me. "Or are you scared someone from Karsix is going to run all the way out here"—he pantomimes mockingly with his fingers—"and cough on you?"

I draw myself taut. "I've been checking it. I simply think we can afford to keep moving. More distance between us and Karsix isn't going to hurt."

In reality, I have no idea how close we are to the surface. I brought a barometer, but I haven't bothered looking at it. At least in some small way, Sean's right. I am afraid we're too close to Karsix. If we made it out, that means others might be able to as well. If someone infected catches up with us, that's it. We're dead. There is no cure, and there haven't been any survivors. So he can mock me all he likes. I'm not going to get this far and die now.

He has the gall to laugh at me. "You are such a liar. You haven't pulled any barometer out."

"You haven't either." If he had, surely I would have seen it.

He holds up a chain around his neck, a hollow glass pendant the shape of a U dangling below. Inside, quicksilver fills from the top of the left side to halfway up the right. He's right; we are close to the surface. In Karsix, the quicksilver would be compressed to about the middle. The higher we go, the more the U will fill up.

"Happy?" A cocky smile curls his lips, and one brow rises.

I cross my arms, looking back the way we came. Four days out, Leavi. Four days out, through the Dead District, past a tunnel split, hidden in a side passage. No one's going to make it that far. No one's going to find us. Surely.

"Fine," I say, still looking off.

Sean nods, smug, and moves into the side tunnel.

As we wind through the passage, the sound of trickling water falls against my ears. I wonder if Sean noticed it when he picked this spot to stop or if he just got lucky. We'll need to hole up here for at least forty-eight hours to complete the quarantine, and since we'll be stationary, we'll need running water. Plus, where there's water, there's moss.

When we get into the room, I signal Sean to put his lantern away. He doesn't argue, whether because he agrees or because he was going to do it anyway, I'm not sure. Probably the latter.

The room shines with a white fairy-glow. Moss blankets the sides of the whispering stream, and the dancing water glints as though winking at us. In the rill, I'm surprised to see fish with functioning eyes rather than the blind types that usually thread their way through underground streams.

In puddles against the bank, cave frogs squat, casting their own tiny green glow. Water moths dart above the waves, their shimmery white pattern helping them to blend into the mossglow. Here and there, a pink tongue flicks out or a fish darts up from the water, and a moth disappears, its natural camouflage having failed it.

One rock toward the end of the room creates a barrier the stream gently waterfalls over, forming a slightly calmer pool before the water narrows back out and flows away. Hanging over the pool, tiny cavefisher crustaceans dangle the bobbing antenna they use as bait, hoping to catch an unlucky minnow.

Entranced, I step forward. Even at only sixteen, I've traveled more than the common undergrounder, studying the life forms of the High Valleys and its caves. However, I've never seen a haven so rich with life in an area so devoid of sunlight. This cave is like a whole world unto itself.

Suddenly, I'm grateful Sean forced the stop. That I could have walked by and completely missed this is unthinkable.

His gaze on me, I collect myself. Out loud, all I give him is an even, "This is a good place to stop." In return, he nods, and we set up camp.

It's going to be a long two days.