But before Alexei can finish, we hear it: a faint scraping, the sound of small rocks being ground into dirt as something heavy moves across an ancient floor.

We spin in time to see that the wall is moving again, closing, locking us in. Alexei races toward the entrance, but he and I have wandered farther inside than we realized, and even with his long strides, I know that it’s too late.

A second later the wall closes, trapping us inside the black.

“No!” I yell, as if that can make the wall open again.

There must be a trigger, I think. I pray. But the wall is almost solid stone, and on this side the pieces of the puzzle aren’t moving, aren’t working. If there’s a trigger to open the door I can’t find it, and as my hands move over the stones, I feel my fingers scrape — my hands bleed. Panic blooms inside me.

“No,” I say, almost to myself. “No. No. No.”

Darkness surrounds us. I realize too late that I’ve dropped my flashlight, and it’s started to roll away, faster and faster. The floor must slope downward, because the flashlight is picking up steam, and a new kind of panic fills me.

I jump to my feet and race across the floor, chasing after the rolling beam of light.

Then the beam flashes across … nothing.

I can sense as much as see the flashlight teeter, tipping, falling away, but I dive, sliding through the dust and the dirt, and grasp the end just as it falls over the edge of the cliff.

And then it hits me: We’re on the edge of a cliff.

It’s not a long room or a corridor; it’s a dead end, and I can feel myself slipping, sliding. I claw against the air as if I can propel myself backward, but then Alexei’s arms are around me, jerking me back into the safety of his chest.

“I got you.” Alexei breathes against my temple. “You’re safe. You’re well.”

We aren’t well. We’re trapped, and I know it.

Behind us, there’s an ancient doorway that is closed. Locked. In front of us is a sharp drop to nowhere.

Only then do I feel the real blackness descending.

My breath comes too hard. Even though my flashlight is bright in the total darkness, I can feel my field of vision starting to close in. My heart is pounding too hard inside my chest. It’s going to burst free and I’ll never be able to stop the bleeding.

“Grace.” Alexei’s voice is too far away. “Gracie!”

Alexei has seen me have an attack before, so I don’t even bother being embarrassed. What use would that be when I know I’m going to die here on this dirt floor in a place where no one besides Spence has been in decades? Maybe centuries.

Our friends are on the island. Our friends will eventually miss us, I know it in my head. But in my gut I know that they may never find this room. They may never open the door. This place that looks and feels so much like a tomb is going to serve as ours, I’m just certain.

And that’s when I begin to rock. I try to slow my breathing. I try to tell myself that there’s no reason to panic. Not yet. I have to think. I have to move. I have to fight.

The door behind us is closed, locked. In front of us there’s a sharp cliff and a long way down — into what, I do not know. I may be the girl who jumped off the great wall of Adria, but even I have my limits.

“If we die,” I say, not knowing where the thought comes from, “it’ll kill Jamie.”

“There’s a way out, Gracie. There has to be. And we’re going to find it.” Alexei turns with my flashlight and starts scanning the space. In front of us, there’s nothing but a sheer cliff and an expanse of black. The secret door and hidden chamber must lead into some kind of massive cavern, and we are standing on a ledge so high that we’ll never find our way down, so Alexei turns back to the way we came. The light plays over the walls and the ceiling, the dusty, cold stone floor.

“Wait!” I yell, just as Alexei freezes. Something small and white lies in the dirt — something decidedly man-made and a few thousand years out of place.

“What is that?” Alexei asks.

“It’s a phone.” I crawl toward the wall and pick it up.

“Is it Spence’s?”

“No,” I say, examining the ARMY cell phone cover that I got my brother for Christmas. “It’s Jamie’s. He told me he lost it the night of the party.”

Frantically, I try turning the phone on. It comes to life, almost fully charged, but of course there is no signal here, so far from the mainland and locked in this place so dark and deep.

“Has Jamie been here?” Alexei sounds amazed, and for a moment I’m confused. Then I remember.

“No. Spence was wearing Jamie’s jacket. It must have fallen out of the pocket when he was down here. That’s why Jamie couldn’t find it even after … It wasn’t on Spence’s body.”

For the first time, my panic wanes. Breath comes easier now, and I feel steady, certain.

We found Spence’s body. We saw it wash up on the beach. So, one way or another, Spence made it out of this dark chamber. The only question is how.

“If Spence was here,” I say, looking up at Alexei, “then he made it out.”

I take back the flashlight and crawl on my knees, inching toward the sharp edge of the cliff. My light plays across the stone on the far side of the huge ravine, thinking there might be some other passage. Maybe there’s a bridge.

And then I see it: a staircase. It’s rickety and ancient — the stairs just a few inches wide — but they’re there. And they stretch, spiraling, leading to whatever lies below.