THE IMPOSSIBLE CHOICEThe air in the armory had grown so cold I could see my own breath. It came out in little white puffs, disappearing into the dark. I clutched the sharpened piece of metal I’d found earlier. My fingers were stiff, and my heart was thumping so hard against my ribs it felt like a trapped bird.

I knew the change in shifts was coming. I’d heard the distant sounds of the camp—men laughing, the clink of armor, the smell of woodsmoke. But inside these stone walls, I was ...