A murmur passed among them, and they stood up and quickly scattered. Their sudden movement knocked something loose in me and I found my voice again and shouted for them to wait, but they were already pounding the floorboards toward the door. I tripped through the wreckage and stumbled blindly across the stinking basement to the stairs. But by the time I made it back to the ground floor, where the daylight they’d stolen had somehow returned, they had vanished from the house.

I bolted outside and down the crumbling brick steps into the grass, screaming, “Wait! Stop!” But they were gone. I scanned the yard, the woods, breathing hard, cursing myself.

Something snapped beyond the trees. I wheeled around to look and, through a screen of branches, caught a flash of blurred movement—the hem of a white dress. It was her. I crashed into the woods, sprinting after. She took off running down the path.

I hurdled fallen logs and ducked low branches, chasing her until my lungs burned. She kept trying to lose me, cutting from the path into the trackless forest and back. Finally the woods fell away and we broke into open bogland. I saw my chance. Now she had nowhere to hide—to catch her I had only to pour on the speed—and with me in sneakers and jeans and her in a dress it would be no contest. Just as I started to catch up, though, she made a sudden turn and plunged straight into the bog. I had no choice but to follow.

Running became impossible. The ground couldn’t be trusted: It kept giving way, tripping me into knee-deep bog holes that soaked my pants and sucked at my legs. The girl, though, seemed to know just where to step, and she pulled farther and farther away, finally disappearing into the mist so that I had only her footprints to follow.

After she’d lost me, I kept expecting her prints to veer back toward the path, but they plowed ever-deeper into the bog. Then the mist closed behind me and I couldn’t see the path anymore, and I began to wonder if I’d ever find my way out. I tried calling to her—My name is Jacob Portman! I’m Abe’s grandson! I won’t hurt you!—but the fog and the mud seemed to swallow my voice.

Her footprints led to a mound of stones. It looked like a big gray igloo, but it was a cairn—one of the Neolithic tombs after which Cairnholm was named.

The cairn was a little taller than me, long and narrow with a rectangular opening in one end, like a door, and it rose from the mud on a tussock of grass. Climbing out of the mire onto the relatively solid ground that ringed it, I saw that the opening was the entrance to a tunnel that burrowed deep inside. Intricate loops and spirals had been carved on either side, ancient hieroglyphs the meaning of which had been lost to the ages. Here lies bog boy, I thought. Or, more likely, Abandon hope, all ye who enter here.

But enter I did, because that’s where the girl’s footprints led. Inside, the cairn tunnel was damp and narrow and profoundly dark, so cramped that I could only move forward in a kind of hunchbacked crab-walk. Luckily, enclosed spaces were not one of the many things that scared the hell out of me.

Imagining the girl frightened and trembling somewhere up ahead, I talked to her as I went along, doing my best to reassure her that I meant no harm. My words came slapping back at me in a disorienting echo. Just as my thighs were starting to ache from the bizarre posture I’d been forced to adopt, the tunnel widened into a chamber, pitch black but big enough that I could stand and stretch my arms to either side without touching a wall.

I pulled out my phone and once more pressed it into service as a makeshift flashlight. It didn’t take long to size up the place. It was a simple stone-walled chamber about as large as my bedroom—and it was completely empty. There was no girl to be found.

I was standing there trying to figure out how the hell she’d managed to slip by when something occurred to me—something so obvious that I felt like a fool for having taken this long to realize it. There never was any girl. I’d imagined her, and the rest of them, too. My brain had conjured them up at the very moment I was looking at their pictures. And the sudden, strange darkness that had preceded their arrival? A blackout.

It was impossible, anyway; those kids had all died a lifetime ago. Even if they hadn’t, it was ridiculous to believe they would still look exactly as they had when the photos were taken. Everything had happened so quickly, though, I never had a chance to stop and wonder if I might be chasing a hallucination.

I could already predict Dr. Golan’s explanation: That house is such an emotionally loaded place for you, just being inside was enough to trigger a stress reaction. Yeah, he was a psychobabble-spewing prick. But that didn’t make him wrong.

I turned back, humiliated. Rather than crab-walking, I let go of the last of my dignity and just crawled on my hands and knees toward the gauzy light coming from the mouth of the tunnel. Looking up, I realized I’d seen this view before: in a photograph in Martin’s museum of the place where they’d discovered the bog boy. It was baffling to think that people had once believed this foul-smelling wasteland was a gateway to heaven—and believed it with such conviction that a kid my age was willing to give up his life to get there. What a sad, stupid waste.

I decided then that I wanted to go home. I didn’t care about the photos in the basement, and I was sick of riddles and mysteries and last words. Indulging my grandfather’s obsession with them had made me worse, not better. It was time to let go.

I unfolded myself from the cramped cairn tunnel and stepped outside only to be blinded by light. Shielding my eyes, I squinted through split fingers at a world I hardly recognized. It was the same bog and the same path and the same everything as before, but for the first time since my arrival it was bathed in cheery yellow sunlight, the sky a candy blue, no trace of the twisting fog that, for me, had come to define this part of the island. It was warm, too, more like the dog days of summer than the breezy beginnings of it. God, the weather changes fast around here, I thought.

I slogged back to the path, trying to ignore the skin-crawly feeling of bog-mud gooshing into my socks, and headed for town. Strangely, the path wasn’t muddy at all—as if it had dried out in just a few minutes—but it had been carpet-bombed with so many grapefruit-size animal turds that I couldn’t walk in a straight line. How had I not noticed this earlier? Had I been in some kind of psychotic haze all morning? Was I in one now?

I didn’t look up from the turdy checkerboard that stretched out before me until I’d crossed the ridge and was coming back into town, which is when I realized where all the mess had come from. Where this morning a battalion of tractors had plied the gravel paths, hauling carts loaded with fish and peat-bricks up and down from the harbor, now those carts were being pulled by horses and mules. The clip-clop of hooves had replaced the growl of engines.

Missing, too, was the ever-present buzz of diesel generators. Had the island run out of gas in the few hours I’d been gone? And where had the townspeople been hiding all these big animals?

Also, why was everyone looking at me? Every person I passed stared at me goggle-eyed, stopping whatever they were doing to rubberneck as I walked by. I must look as crazy as I feel, I thought, glancing down to see that I was covered in mud from the waist down and plaster from the waist up, so I ducked my head and walked as fast as I could toward the pub, where at least I could hide in the anonymous gloom until Dad came back for lunch. I decided that when he did, I would tell him straight out that I wanted to go home as soon as possible. If he hesitated, I would admit that I’d been hallucinating, and we’d be on the next ferry, guaranteed.