My heart slammed in my chest as I ran. My breath was ragged and labored. I couldn’t think straight, couldn’t focus on anything except on my need to get away, as quickly as possible. Find somewhere to hide, where GSAF wouldn’t find me. Somewhere to think, to figure out how exactly I was going to get myself out of this disaster that I had managed to blunder my way into.

I was nearly to the edge of town when I heard a telltale buzz above me. My head jerked skyward in a panic. Faintly, I could see moonlight glinting off the nose of a GSAF security drone. It was hot on my tail. How had they found me so quickly? I’d left my palmtop in Emil’s apartment! Was there some other piece of electronics on me that I wasn’t thinking of? Some other way of tracking me? Had Joseph Condor bugged me this afternoon in the office? Oh, Cristo, I bet that was it. Was it really so important to keep this stuff from the dig site a secret that they’d bug a teenager?

I couldn’t stop to think about it. If I waited any longer, the drone would have me in its sights and I’d be done for. I wasn’t sure if the aircraft above my head was loaded or not—I mean, really, is a high school student a big enough threat to an interplanetary organization that they’d need to take me out?—but after all the crap they’d put me through in the last two days, I wasn’t going to take any chances.

I clutched Podkayne of Mars against my chest so tight that the corner of its spine dug painfully into the palm of my hand. But the pain just prodded me forward, into the foothills.

Emil’s map indicated the entrance should be around here, but I’d never been to this part of town before. What if Emil was wrong? What if he’d set me up? Or what if GSAF had learned of the cave’s existence, and sealed it the same way they did the crater? What if there were suits waiting just inside, ready to take me away and make sure that I was never heard from again?

Then I saw it—a shadow in the darkness. Under a narrow ledge, half-covered in overgrowth and bramble, there was a gash in the hillside.

The buzzing sound of the drone grew closer. It was almost on top of me. There was no time to reconsider.

I dove into the crevice. The rock walls pressed against me. I barely managed to fit in the space between them. Desperately, I wrenched my body forward as hard as I could and squeezed into the cave beyond.

It was far darker in here than it had been outside. Even without the lights of the city to guide me, the starlight had been better than the pitch blackness of the caverns in the hillside. I’d have killed for my palmtop then. How was I supposed to light my way without it?

I sat in the darkness for several long minutes, listening. The drone passed overhead. The buzz of its blades grew loud, then faded, like it was moving away.

Then there was nothing but the sound of my own breathing and my heart beating in my ears.

They’re gone. Breathe, Isaak.

The silence let the thoughts flood in. My mom was going to kill me, if I ever saw her again. I wondered what would happen to Henry, and to Tamara. Henry was probably as done for as I was—most of my texts were from him. But maybe they wouldn’t connect Tamara, after all. Maybe she’d be safe. Please, let her be safe.

I focused on the muffled sensations of the cave. Soft drips of water echoed faintly in the distance. Cold air moved gently against my face, and I realized that I could hear wind moving through the tunnels of the cavern. Just how long were these tunnels, anyway? Emil’s map had shown them stretching into the mountainside, but I hadn’t looked at it carefully enough to see where they’d ended. Maybe there was an exit, somewhere else in the hills.

I could only pray that I’d find my way out before GSAF found their way in.

Finally, I started to inch my way forward, back toward the crevice I’d entered the cave through. I couldn’t get anywhere in the dark like this, with no way to light my path. I’d have to go back, think of something else.

I was just about to try to squeeze back out through the crevice when I heard the buzz once more. The drone was circling back. I froze, unable to move, unable to think.

The next sound I heard was even more ominous than the drone.

Voices.

Right outside the cavern’s entrance.

Any second now, a light would shine through that narrow crack, and the suits would find me. There was nowhere to go, nowhere to hide. Nothing I could do. It was over.

Unless I went forward.

I felt my way through the tunnel as silently as I could manage. The rock walls were cold and surprisingly smooth. It was narrow at first, just barely wide enough for my body to squeeze through, but as I moved along, the tunnel began to widen.

Soon I saw light ahead of me. I thought that this must be an opening, an exit back out into the outside world. I rushed forward, and suddenly found myself in a larger cavern. The light wasn’t coming from outside at all—there was some kind of weird, glowing luminescence all around the cavern. Blue and green speckles blinked all around me, forming strange patterns of light, like stars in the night sky. Or like magic.

It reminded me of vids I’d seen on Speculus of glow worms on Earth. Could they live on Mars, too? At this point, I didn’t think anything would surprise me.

I followed a trail of the glowing dots across the cave. A puddle of water pooled on the ground. I splashed through it, the water licking through my jeans. It was as cold as ice. I scrabbled across, reaching for a thick stalagmite to pull myself back up onto dry land.

My hand didn’t land on rock, though.

I gasped in spite of myself. The sound of my voice echoed across the cavern, and I froze, listening for any sounds of my pursuers approaching, drawn by the noise. There was nothing.

I turned to the stalagmite to investigate. The rock formation was about a meter and a half high, and there was something strewn across the top of it. Fabric. I picked the material up and squinted at it in the dimness.

It was a jacket, made of thick, flame-retardant material. It reminded me of the jackets factory workers in Tierra Nueva often wore. As I ran my fingers across it, I felt something thicker, like a patch. A name badge. I moved closer to a clump of the blue glowing speckles, trying to get a better look. There, I could just make out the embroidered cursive letters—

Raymond.

I nearly dropped the jacket into the puddle, but caught it just in time. This was my dad’s work jacket. He’d been wearing it the last time I’d seen him, standing on the train platform that October day. I took the northbound train to school, and he went east to work. He’d seemed preoccupied. He didn’t say goodbye when I hurried to board my train.

I’d thought, later, it was because he was planning on leaving that day. Heading back to Earth. But he hadn’t boarded a shuttle. He’d come here.

I felt like I was going to be sick.

I clutched the jacket to myself, wandering blindly through the cavern. I was so nauseous, so overwhelmed, that I almost didn’t see it. But then it was right in front of me, and I couldn’t ignore it. Three meters tall and as wide as four people.

The arch.

I drew a ragged breath. It was here. It was really here. And so was Dad’s jacket. He had the key. He must have used the arch. There was no other explanation. But where had he gone?!

I ran my hands over the rough stones, stacked in their corbeled pattern. It looked just like it had on the coin. Unbelievable.

As my skin touched the stone, the arch seemed to vibrate. There was a hum, barely audible. Like some kind of long-dormant power lay buried inside. Could it really be a tesseract?

A louder sound behind me drowned out the arch’s hum. I froze, listening, though my heart pounded so loudly that I could barely hear anything else.

Voices. In the cave. They were coming.

They’d find me.

I didn’t have time to think. If I’d been thinking straight, I never would have done it. But I was panicking. All I could think of was Joseph Condor on one side—and my dad on the other.

Maybe he hadn’t abandoned me after all.

In a heartbeat, the key was in my hand. I slipped the coin out of my pocket and, fumbling in the dark, found the round recess. Just the right size. Just like Emil said.

I pressed the coin into the divot, and it clicked.

The key was rusty and corroded, but it must have still worked, because when I pressed the coin into it, it sprang open, the hinges along the edges unfolding again and again, from a four-pointed star into a shape too complicated to name. Though its outer casing was metal and worn, the inside of the key was bright and new-looking. Diodes on the interior lit up, glowing purple and emitting a strange, humming whir of sounds, resonating with the sounds from the arch. When I touched one with my finger, it sparked.

The arch began to flicker, like a fluorescent light that’s been switched off for far too long. Between the joints of the stone, bright light emanated, pulsating, crackling with electricity.

“Over here!” I heard a voice in the distance. “He must have come this way!”

The light of the arch grew brighter and brighter. It was blinding to look at. The arch had transformed into a doorway of light, and the key grew so hot it burned my hands.

The pounding feet behind me grew louder and louder.

I squeezed my eyes shut and stepped into the light.

The force of it was awful. It felt like my body was being crushed by the weight of a giant, squeezed down small enough to fit through the eye of a needle. I wanted to scream, but I couldn’t feel my lungs, couldn’t find my vocal cords. I was dying. I had to be.

Then suddenly the light was gone, and my voice was back, my shouted agony ringing in my ears and burning my throat. When the screaming stopped, I tried to breathe, but the air was thin—it burned worse than the screaming had.

I was flat on my back. I opened my eyes to see fiery orange clouds swirling above my head. The wind pelted me with red dust. I wasn’t in the cave anymore. But this wasn’t Earth, either. Where had the door of light taken me?

I struggled to my knees, trying to draw a breath but coming up empty. Around me was a desert plateau, strewn with gray boulders that were tinged with reddish-orange stripes. Above it all, I could see something—a dome-shaped building with glass walls, like a greenhouse.

I tried to move toward the building, but I felt disoriented, like I was walking through a dream world. I finally managed to stand, and the plateau loomed up toward me sideways. It was like trying to move in a fun house. If only I could breathe.

If I could get to the building, I might be able to find help. I had to get help. I was going to die if I didn’t get air soon.

In front of the building—there was a person. It wasn’t my imagination. There was a someone standing just twenty meters away from me. She looked like an old woman, with thick white hair braided around her head in a spiral. If she would just turn this way, she’d see me.

“Hey,” I tried to call out, but no sound came. The lack of oxygen stole my voice once again. I waved my arms, but another wave of nausea hit me. And still the woman did not look my way.

“Please,” I whispered, falling over on to my side. My vision swam, the building swirling together with the rocks and the ground and the woman and the ever-darkening sky.

The sky. I blinked, certain I was imagining it. But it was still there even as my vision blurred to black.

Beyond the clouds, larger than the sun, a huge, bright moon burned overhead.