Three centuries ago, the Long Winter drove the frost-dwarf clans south across the Shatter — a 200-mile rift valley splitting the mountain range in two. The crossing was barely survivable then. Since, geological instability has made it worse. No one has crossed in living memory. The northern holds are considered dead.

Then a resonance-pulse reaches Iron-Peak Hold — a living distress signal transmitted through deep-earth harmonics from Kaldheim: We are still here. We are dying. Send help.

Expedition leader Revka Shard-Born has spent twenty years arguing that the north survived. The pulse proved her right, and now she has one chance to prove the crossing is possible.

Her team: a geologist who treats the Shatter like a living creature, a rope-master haunted by the last failed expedition, a medic running from a failed marriage, a young cartographer on her first real assignment, and a deep-walker scout who hasn't spoken above a whisper in a decade.

Between them and Kaldheim: the Descent, the Vents, the Floor, the Floodway, and the Ascent — steeper, colder, more lethal than anything that came before.