WHEN SHE FINISHED, the two sat in silence for a moment, listening to the push of the ocean through the rocks below and the plinking of water dripping from the roof of the cavern. Dim light filtered through the open door at the top of the stairs, and though their eyes had adjusted to the dark, there were still many areas of the room hidden from their view.

“You didn’t think I’d follow you down here if you told me your story first,” said Eli. “Right?”

Josie smiled, trailing the crab with her phone’s glow. The creature crawled back down into one of the pools.

Eli squeezed his knees together. “So there really are other people on the island? Other than the wedding party?” He stared into the dark patches of shadow all around the space, as if one of these people were watching them right at this moment. He couldn’t stop himself from standing up and taking a step toward the staircase.

“But why would the caretaker lie?” Josie stayed put, stuck in her head.

“And where did the girl go?” Eli asked. “Are you sure there wasn’t some sort of secret door in the closet? The house seems like the type that might have a few of those.”

“I checked. I swear. The walls were solid. I mean, maybe she slipped away when I stepped out to look for Bruno.”

“And you’re sure you weren’t, like, dreaming? You were lying on the bed, right? Maybe you’d fallen asleep?”

“I saw her as clearly as I see you right now.”

“Maybe we could see better if we went outside.”

“What’s the difference between what I saw and what you heard?” Josie asked, not moving.

“Well … I dunno. Maybe there’s something about this island that messes with our senses.”

Josie squinted. “Something? Like what? Magic?”

“Not magic. I mean, aren’t there certain frequencies or smells or even shapes that we look at that can be disorienting? You know, scientifically?”

Josie snorted. “The girl in my room didn’t look like a scientist.”

“You know that’s not what I mean.”

“Let’s just get out of here. My battery won’t last much longer.”

“My dad’s going to flip if he figures out I went off by myself.”

“But you’re not by yourself.” Josie smiled. “I’m here. I’ll protect you.”

“Right.” Eli smiled back sadly. “From my dad? Or from the strangers on the island?”

“Whoever we run into first. Come on. If everyone’s calmed down about the cloudy sky, maybe we can check in with the caretakers and ask them about this old fort.”

As Josie swung her flashlight around the room one last time, Eli saw something glimmer in the corner, by the crevice where the sound of the whirring surf emanated. “Wait. What’s that over there?”

“Over where?”

Eli took a deep breath and stepped lively across the floor, avoiding the pools, telling himself, One minute more. One minute, and then we’re gone. “Would you shine your light there?” He pointed at the ground where the crevice met the wall.

Josie provided him with the light, and something in the cracked wall glinted again. Eli crouched, leaning closer to the opening. From down in the darkness, he could make out the sound of water burbling and bubbling, washing against the hidden stones that were surely covered in the same barnacles and slime that had made their way up into the cave’s shallow pools. But the sounds weren’t what had his attention. In a tight gap in the side of the crack, a few inches up from where the wall met the floor, was a small piece of metal.

Josie wandered closer, providing illumination, as Eli reached out and grabbed the edge of the object. By wiggling it up and down, back and forth for a few seconds, he managed to work it loose. Soon, it fell into his palm. It was circular in shape, and though it was clearly metal, brass or copper, the sections that weren’t burnished had corroded into the same dull green color as the seaweed in the pools behind them, as if the object had been trapped down in this cave for many years.

“Looks like a coin,” said Josie, standing over Eli’s shoulder. “Maybe it’s worth something?”

“Not a coin.” Eli turned the object over. “A button.”

“A button? Like on a shirt?”

“Like on a coat. Or a uniform maybe. Look, you can just make out a symbol on the front.” A slight indentation marked the button’s surface. It looked sort of like a cross. But different.

Josie gasped. “I’ve seen this before. In my history class last year.”

Eli’s stomach squelched, as if someone had reached inside and squeezed it. “Everybody has seen this before. It’s a swastika.”