The night the frost started creeping across the inside of their bedroom window, Thomas stopped pretending their house could save them.

The blue frost did not climb the walls like normal ice; it moved with a terrifying, silent intent, spreading along the mortar lines in patterns that looked almost like written characters. Wherever the blue needles touched, the brick went cold instantly, the heat dying out as if a light had been switched off.

The crowd in the kiln panicked. People scrambled away from the walls, huddling closer and closer to the center of the room, their brief illusion of safety shattered.

"We have to go down. Now," Nicholas said, his voice tight.

Thomas nodded. He grabbed his lantern, his cold chisel, and his leather bellows. He looked at Claire, who was holding both Matthew and Lucy in her arms, her eyes filled with a desperate, unspoken plea.

"Stay in the center of the room," Thomas told her, his voice softening as he pressed his forehead against hers. "Keep the children close to the oven mouth. The core is directly beneath it; it will be the last place to go cold."

"Come back to me," she whispered. "Please, Thomas."

"I will," he said.

Thomas, Nicholas, and Arthur Vance—who had thawed enough to hold a lantern—descended the rusted iron ladder into the subterranean chamber.

The heat in the lower vault was different now. It was no longer the dry, comfortable warmth of a summer afternoon; it was a heavy, moisture-laden heat that felt like a swamp before a storm. The steam was rising from the floor, condensing on the cold stone ceiling and dripping down like warm rain.

When they reached the bottom, Nicholas let out a low, horrified whistle.

The black metal well in the center of the room was nearly covered in the blue frost. The four massive chains holding the heart were encrusted with thick, jagged spikes of blue ice that seemed to glow with their own pale, predatory light.

The heart itself was pulsing erratically now, its crimson glow dimmed, struggling to break through a thick, translucent shell of blue ice that had already covered more than half of its surface. Each pulse was accompanied by a wet, grinding sound, like teeth scraping against stone.

"It’s beautiful," Arthur whispered, his eyes wide as he stared at the glowing, frozen heart. "It looks like... like a jewel."

"It’s a parasite," Thomas said, stepping up to the edge of the well. He took his bellows and aimed the nozzle at the blue ice near the lowest chain. "Nicholas, help me with the draft. We need to clear this chain first. If the weight of the ice snaps the support, the core will fall into the shaft below, and we'll never get it back."

Nicholas stepped up beside him, his massive chest heaving as he began to pump the heavy leather bellows, forcing a concentrated stream of air toward the ice.

But the moment the air struck the blue crystals, something went wrong.

The ice did not melt.

Instead, it seemed to react to the draft, the needles of frost instantly growing, reaching out toward the nozzle of the bellows like living fingers. A sharp, high-pitched hum—like the sound of wet glass being rubbed with a finger—vibrated through the chamber, so loud it made Thomas’s ears bleed.

"Stop!" Thomas yelled.

But it was too late.

The blue frost had already climbed the nozzle of the bellows, freezing the leather instantly, turning the flexible material into a brittle, gray shell that shattered into a hundred pieces under Nicholas’s grip.

The blacksmith stumbled back, his hands stinging from the sudden, intense cold that had travelled up the wooden handles.

"What is that stuff?" Nicholas gasped, staring at his frozen, ruined tool. "That's not ice. Ice doesn't fight back."

"It’s drawing the heat," Thomas said, his face pale as he watched the blue frost on the stone heart grow thicker, the crimson pulse skipping another beat. "It’s not just freezing the world; it’s eating the warmth. Every time we try to warm it, we’re just feeding it."

Arthur Vance stepped closer, his hand reaching out toward the glowing blue chains. "If we can't warm it... then how do we stop it?"

"We don't warm it," Thomas said, his eyes narrowing as he stared at the jagged, raw surface of the stone heart where the crimson light was still visible beneath the ice. "We have to cut it out. We have to treat it like a flaw in a block of marble."