Commander Borin Ash-Spire was once the Magma-Forge's most brilliant tactician. Now he commands Black-Iron Watch—a crumbling fortress at the edge of the frozen world, staffed by exiles, criminals, and castoffs the dwarven kingdom would prefer to forget.

Then the prisoner arrives. Sylvi Ember-Heart is a pyromancer whose uncontrollable fire once threatened to bring down an entire forge. Chained in adamantine, sick and shivering, she's been sent to the one place her heat might be useful—or where she'll die quickly enough to stop being a problem.

But the cold is changing. An unnatural blizzard is creeping southward, and within it move creatures of ice and shadow that feed on warmth and life. The Frost-Ghouls have awakened, and they're not just attacking—they're hunting.

To survive, the disgraced commander and the terrified pyromancer must learn to trust each other. Borin must teach Sylvi that fire isn't a curse to be suppressed but a force to be directed. And Sylvi must find the courage to stop fearing herself.