I sighed and opened my eyes. It must be long gone by now, buried in some landfill where I’d never find it. I was just starting to get back to my feet when my eye caught on the hatch to the crawlspace on the ceiling of the closet. We’d never stored anything up there, since it was loaded with insulation and Mom was worried Celeste or I would get sick. But I shoved the hatch open now and, stretching up on my tiptoes, reached inside.

I felt around for a few seconds, encountering nothing but dust and bits of fiberglass. But then my fingers struck something hard and metal.

I pulled the object out. It was the box.

It looked like some kind of vintage lunch box you’d see in flix, with the remnants of a painted cartoon character on its lid. I didn’t know how old it was, but I knew he’d brought it from Earth. The hinges were rusty, which made opening the lid difficult, but I finally managed to pry it open. There was all the junk I remembered, all the weirdly personal objects that seemed strange to leave behind. Little knick-knacks and trinkets, and a handful of memory cards and flash drives.

And among all of Dad’s Dad things, shoved up in the corner, was the coin.

You could tell right away that it was ancient. It was made out of some kind of metal, but it was all corroded and discolored, kind of a greenish hue now. Its reverse was engraved with nine circles, each differently sized. The front face of the coin, meanwhile, had three marks along the upper rim, but they were too worn for me to make out. They didn’t quite look like writing; more like pictures, or maybe symbols of some kind.

And beneath these markings was an engraving of an arch. It looked bigger than the one that I’d seen at the dig site—that one was only waist high, and the one depicted on the coin showed a figure standing beneath it, as if passing through a doorway—but the pattern of the flat-topped stones was identical, sort of an upside-down-V-shaped archway.

I hadn’t thought much about the coin at the time Henry and I found the box. We’d come across it, buried in the garden, while we were supposed to be yanking up spider weeds to get the ground ready for Mom to plant the new experimental seeds she’d developed to grow during the long Martian autumn. It had been clear when we’d got the lid open that it was Dad’s stuff, but there was so much else in the box that I hadn’t dwelled on the coin too much. I guess I’d figured he had probably gotten it from one of his friends at the factory. You’d never believe the kind of weird junk they’d brought with them from Earth.