The dripping green eye on the Ember’s oak hull seemed to stare back at them through the cold mist, its bioluminescent algae bleeding slow, emerald tears into the black water of the waterfall pool. The waterfall behind them thundered like a collapsing glacier, but to Cormac Reed’s ears, that deafening roar was merely a backdrop. Beneath the weight of the cascading water, his heightened acoustic sensitivity picked up a far more terrifying sound: the rhythmic, synchronized slide of narrow paddles cutting through the dark current beyond the cavern’s lip.

They were surrounded.

"Garrick," Cormac whispered, his voice a low, gravelly rasp that barely carried over the deck plates. "Muffle the boiler. We cast off now. No lights."

Garrick Vance, his broad shoulders slick with sweat and condensation despite the sub-zero chill, nodded grimly. He slipped back into the engine hatch, his movements silent and practiced. Below deck, the muffled hiss of the steam engine died down to a low, vibrating hum. The Ember drifted out from the shelter of the frozen waterfall, her bow pulling hard to port. The copper plating on the left side of the bow was severely dented from their collision in the Drowning Pool, creating a constant, dragging pocket of turbulence that fought Cormac's single-handed grip on the heavy oak tiller.

Cormac stood at the stern, his teeth clenched against the cold and the dull, burning agony radiating from his right arm. His right hand, wrapped in scorched, mud-crusted bandages, was locked in a tight, useless claw shape—a permanent reminder of the boiling steam bypass he had manually forced in the cold vault. He could not use his fingers to grip the tiller or adjust the rigging; his entire right arm hung like a dead weight under his caribou-skin coat. He had to rely entirely on his left arm, wedging his body against the wooden frame of the tiller to keep the vessel straight.

"Toby," Cormac muttered, his eyes scanning the absolute blackness ahead. "What does the compass show?"

Huddled near the main mast, Toby Miller was shivering in his damp wool coat, his brass-rimmed spectacles fogged to a solid white. He reached into his pocket and pulled out the Thorne Compass, shielding its face with his gloved left hand. The thermal-magnetic needle inside the brass casing was spinning slowly, its tip vibrating as it struggled to align with the geothermal currents of the lower caverns.

"The... the thermal readings are fluctuating, Cormac," Toby whispered back, his teeth clicking together. "The temperature is rising, but the sulfur levels are throwing the magnetic needle off. We’re entering the transition zone."

They drifted into the Silt-Walker Outskirts.

Almost instantly, the dry, biting chill of the glacial caverns began to shift. The air grew damp, heavy, and suffocatingly warm, thick with the stench of rotten eggs. Volcanic sulfur crystals clung to the jagged basalt walls like yellow frost, their pale coloration offering no light in the pitch-black tunnel. A dense, blinding sulfur fog rolled over the water, reducing their visibility to absolute zero.

At the bow, the lookout Finn held his heavy brass spyglass to his eye, but the thermal lens was completely clouded by the damp humidity. "I'm blind, Cormac!" Finn hissed back. "The fog is too thick. I can't see five feet ahead of the bow. If there are icebergs or rocks, we're going to strike them."

"Owen, dim the Hearth-Lantern," Cormac commanded.

Owen, the lantern-keeper, quickly adjusted the brass shield of the primary lantern. The faint blue spark inside—the last ember of Oakhaven’s fire—was instantly muffled, its light reduced to a tiny, pinpoint glow that barely illuminated the wet deck plates. The cracked glass lens of the lantern creaked under the rapid temperature shift, a sound that made Cormac’s heart tighten. If that glass shattered completely, the damp, sulfurous air would choke the flame, leaving them in absolute darkness with no way to reignite it.

"We drift blind," Cormac said, closing his eyes. "Listen to the water."

Without his sight, Cormac’s world shrank to the sounds of the cavern. He listened to the low-frequency hum of the river, the slap of the current against the basalt banks, and the sluggish drag of their dented bow. But beneath those familiar noises, he heard a new, terrifying frequency: a sharp, metallic whistle cutting through the sulfur fog from the high cliffs above.

"Spears!" Cormac roared, throwing his weight against the tiller. "Hard to starboard!"

He didn't wait for the crew to react. He wedged his body against the tiller, using his shoulder to force the heavy oak wood to the right. The Ember groaned, her dented bow fighting the sudden shift in momentum, pulling sluggishly through the dark water.

Thwack! Thwack! Thwack!

A volley of heavy, carved bone spears rained down from the dark cliffs, their volcanic obsidian tips slamming into the deck plates. One spear embedded itself inches from Toby’s foot, its shaft vibrating violently. The spears were carved from the bones of deep-water leviathans, their tips designed to pierce heavy caribou-skin diving suits with ease.

"They're on the ledges!" Boran the Stout shouted, scrambling to the bow ballista. He wound the heavy steel winch with a frantic, metallic clatter, aiming the copper-plated launcher into the blind fog above. "I can't see them, Cormac! Give me a target!"

"No, Boran! Hold your fire!" Cormac called out. "The acoustic vibration will bring the ceiling down!"

But Boran, driven by survival panic, ignored the order. He pulled the release lever.

The heavy iron bolt launched into the darkness with a thunderous twang. A second later, a loud crash echoed from the stone ceiling as the projectile smashed against a fragile ice shelf. The impact triggered a localized cave-in, sending a shower of sharp ice-needles and basalt rock splinters raining down onto the deck. One large shard struck the port gunwale, cracking the wood and throwing the boat off balance.

"The steam line!" Garrick screamed from the engine hatch.

Before Cormac could steer away, a second volley of bone spears whistled through the mist. One obsidian-tipped shaft struck the copper steam pipe running along the deck, piercing the thin metal.

A violent, high-pitched shriek erupted as superheated steam began to vent from the rupture, filling the deck with a blinding, scalding white fog. The sudden release of heat and noise was like a beacon in the dark. On the cliffs above, the Silt-Walker hunters of Sena's War-Band let out a series of clicking, predatory calls. They had located their target.

"They know where we are!" Toby panicked, shielding his face from the escaping steam. "The heat is drawing them!"

Cormac’s mind raced as his scarred lung registered the rapid drop in atmospheric pressure. He knew they couldn't fight a blind battle against camouflaged hunters on their own turf. If they stayed here, the spears would eventually find their mark, or the escaping steam would completely drain their boiler, trapping them in the outskirts. He had to find a safe channel, but the fog was absolute, and the Thorne Compass was spinning uselessly near the sulfur vents.

Suddenly, out of the thick, yellow fog on the opposite bank of the river, a brilliant, green light ignited.

It was not the harsh, destructive flame of the surface dwellers, but a cold, bioluminescent flare that cast a soft, emerald glow through the mist. The light emitted a specific, low-frequency hum that resonated through the water, registering as a sharp thermal spike on Toby’s vibrating compass.

"Cormac!" Toby shouted, pointing toward the green glow. "The compass is locking onto a thermal signature! It’s a concentrated heat source, directly to the right!"

Cormac looked toward the emerald light. Through his acoustic sensitivity, he could hear the water current shifting ahead, flowing smoothly into a narrow, quiet channel behind the flare. It was a guide.

"Garrick, dump the remaining steam to the starboard propeller!" Cormac commanded, his left hand gripping the tiller with white-knuckled force. "Follow that light!"

Garrick threw his weight against the manual bypass valve, ignoring the scalding vapor that hissed around his face. The Ember’s engine let out a final, desperate surge of power. The boat pivoted sharply, her dented bow scraping against a submerged basalt tooth as she slid out of the main river current and into the narrow, hidden channel.

The bone spears clattered harmlessly against the stone walls behind them as the entrance of the channel swallowed the vessel. The thick, toxic sulfur fog began to thin, replaced by a cool, quiet dampness. The sound of the thundering waterfall and the clicking calls of Sena’s hunters faded into the distance.

They had escaped the ambush, but the pressure was far from over. The water in the narrow basalt channel was accelerating, the low-frequency hum of the river dropping to a deep, ominous vibration that suggested a vertical drop was approaching downstream.

Cormac let go of the tiller, his left arm shaking from the physical exertion. He collapsed against the stern rail, his chest heaving as he cradled his useless, bandaged right hand. The skin beneath the scorched wool was cold, the dead nerves offering no sensation, but the bone-deep ache in his wrist remained, a constant reminder of the ticking clock.

"Is everyone alive?" Cormac gasped, looking at the huddling shapes of his crew.

"We're whole, Cormac," Dr. Fiona Glenn said, helping Toby to his feet. "But the boat is scarred, and the steam line is leaking. We won't have enough pressure to fight a strong current if the river drops."

Before Cormac could answer, a soft, scraping sound echoed from the bow deck.

Finn raised his grease lamp, his hand trembling as the weak light cut through the remaining mist.

Standing on the bow of the Ember, having dropped silently from the low cavern ceiling, was a slender figure. Her skin was pale, almost translucent in the dark, and her large, dark pupils were adapted to the pitch-black of the deep. She wore garments made of cured fish-skin that clung to her frame, and in her hand, she held a glowing crystal pendant that emitted the same green bioluminescent light they had followed through the fog.

She looked directly at Cormac, ignoring the weapons the crew scrambled to raise. Her voice, when she spoke, was a low, melodic whisper that carried the weight of the deep earth.

"I am Lyra Dusk," she said, her eyes locking onto the cracked Hearth-Lantern on Cormac's chest. "And I demand to speak with the Fire-Bringer."