Beneath a frozen lake, a long-dormant mechanism revives Sherkaner Underhill’s four-person team—Hrunkner Unnerby, Amberdon Nizhnimor, and Gil Haven—who thaw unevenly inside their hybrid sub/deepness. With oxygen-tight suits, safety/audio cables, and panniers of engineered “exotherm” bacteria, they emerge into the Deepest Dark and begin the trek toward a Tiefer outreach depot.

The team advances in short, painful stages, using exotherms to find and exploit buried organics for heat and air. Sherkaner keeps bearings and fuel flowing, while frostbite worsens for Gil. Overhead, dazzling lights—four searing points and spreading veils—flare across the sky, an unprecedented aurora-like display that briefly warms the ground before fading. Despite awe, Unnerby drives them onward.

They descend a ramp into the depot, a sunblinded field packed with locomotives and armored vehicles poised for the New Sun. Splitting per plan, they plant small charges to collapse canopy sections and launch dye-black mortars, mottling equipment surfaces. The gambit is designed to make exposed metal catastrophically overheat and seize during the first hours of the New Sun, crippling Tiefer readiness.

Retreating, they push hard toward a preidentified refuge, but Haven deteriorates: frost damage and panic give way to Wanderdeep. He repeatedly breaks free, and during a steep ascent he turns frantic and falls to his death despite Amber’s struggle to restrain him. Grieving, the remaining three continue, focused on survival.

They reach a natural animal deepness—home to tarants with food stores—cut through barriers, and secure pools and provisions using their last exotherms. Exhausted and injured (Amber likely to lose hands; Sherkaner numb in several joints), they prepare to refreeze, resealing the entrance. Looking back at the depot stained black, Unnerby questions the plan, and Sherkaner explains the expected New Sun welding/lockup. He predicts future Dark-era colonization, and they descend to face the last peril of uniform freezing.