"Smaug, take us down!"

Kael and Gandalf leapt onto Smaug's back. The dragon tucked his wings and plunged into the abyss.

The chasm beneath Durin's Bridge was no dwarven shaft but a natural rift in the mountain's heart, a throat of darkness that swallowed sight. Even the dwarves of Moria had never found its bottom or measured its depth.

Clinging to dragon scale, Kael and Gandalf felt the wind knife past and sting their faces raw. They fell… fell… minutes blurred. Minutes blurred. Time unspooled into blackness so complete that a hand before the face would vanish.

Just as Kael wondered if they had pierced the world's core, Smaug flared his wings, bled speed, and rumbled, "Master, the Balrog is below. It climbs toward us."

They craned downward. In the lightless gulf a spark flickered, then grew. In perfect darkness, fire is always seen. A whip of flame lashed the cliff. The Balrog hauled itself up the sheer rock as if it were flat ground. The air turned from ice to furnace.

It saw them and bellowed. Then it ran faster, a hurricane of black fire charging up the wall.

Kael pulled his last three fire-protection draughts. One he swallowed at once. One he pressed into Gandalf's hand. The third he tipped into Smaug's jaws.

Smaug shivered as the potion settled. Even the fire in his gut guttered. He coughed smoke and no flame. "Master?"

"Hold it fast. Don't let it escape. If it drops into the deep water, its power will fail, and it won't threaten us."

A heartbeat later the whip snapped up and coiled Smaug's hind leg. Smaug, startled to find the flame harmless, clamped the lash in his teeth and heaved, yanking the Balrog up toward him. Then he twisted, seized the demon, and dragged it off the wall into a dead drop.

The Balrog thrashed and burst a storm of black fire that engulfed the dragon and riders. The draughts kept flesh from searing, but the protection would not last. If the potions failed before the demon did, they would burn.

Locked together, they plummeted. Gandalf's staff had been lost to the fall. With Glamdring in one hand and the Flammifer in the other, he sprang from Smaug's back, landed on the Balrog's shoulders, drove the Flammifer down its spine, and fenced the demon with Glamdring as they fell through roaring wind.

Kael could hear nothing but the scream of air. His eyes watered in the blast. Smaug wrestled. Gandalf struck. Kael gritted his teeth, lifted his staff, and cast to turn speed into stone.

"Finite Levicorpus!"

Their rapid fall turned into a dead drop, as if a great weight had been tied to them. The Balrog's fire streamed behind it in a long, ragged tail. Weightlessness tugged Kael free of Smaug's back. He caught the dragon's tail with both hands and held on.

A wet chill needled his face.

"Master, we're near the bottom!" Smaug cried over the wind.

Sensing water below, the Balrog detonated a wave of heat that wrapped Kael, Gandalf, and Smaug in a sea of fire. Even through the draught, Kael felt the scorch. Flame filled the world, even the breath in his lungs. His cloak kindled. A space bag at his belt popped and tore. Charms, vials, and runes spilled and spun away into the dark.

No time to mourn. Kael tore Aeglos free, hurled himself at the demon's face, and rammed the spear into one blazing eye.

Aeglos erupted with biting power. Half the Balrog's head vanished in a burst of white-cold force.

Fire poured back to re-form its skull. The body was flame given will. While the flame endured, it would not die.

Kael still exhaled in relief. In that instant of ruin the demon's mind had staggered.

They reached the water.

"Arresto Momentum!"

Kael, Gandalf, and Smaug halted a handspan above the black surface, then dropped, avoiding the lethal impact.

The Balrog, with no check at all, slammed into the deep. A mountain of water rose, hissed, and fell as fire met Ulmo's realm.

A heartbeat later Kael, Gandalf, and Smaug crashed into the cold. The pressure clenched the ribs; breath seized. The water bit to the bone. Hearts clenched. Breath seized.

The dark was absolute.

Kael flicked a globe of light into being. Pale radiance showed a vast, still cavern-lake. Smaug beat his wings and floundered. Gandalf rose, swords ready. Across the water, the Balrog thrashed.

Kael scrambled onto Smaug's back before the cold took his strength. Gandalf waded, blade-light flaring.

"Unclean spirit, this is the realm of Ulmo. Here you have no power!" His voice boomed through the flooded vault.

As if in confirmation, the Balrog's flames died into oily black. Power drained away. The demon sagged to a tar-dark shape, still mighty, but diminished to something nearer Gandalf's strength.

"Master, you are here too!" hissed a voice close by.

Herpo slid from the water, eyes shut, scales slick. Joy ran through the Parseltongue whisper.

"Herpo!" Kael grinned despite the cold. "Help Gandalf. Eyes and fangs. Strike and poison it."

The basilisk slipped beneath the surface and arrowed at the demon's legs. Fangs sank in. Venom flowed.

The Balrog snarled and lurched. It could not die from that venom, but its strength sagged again.

Kael whipped his wand. Scattered gear leapt back to him with Summoning Charms. He found Gandalf's staff in the haul.

"Gandalf, your staff!" He hurled it.

Gandalf's eyes lit. He caught it, leveled it, and hammered the demon with a crushing spell that sent it skidding across the dark water.

"Avada Kedavra!" Kael's curse struck the tarry mass and dimmed it further.

Pressed by Gandalf's blade and staff, Kael's killing curses, Smaug's bulk, and Herpo's fangs, the Balrog broke and fled into a narrow, rising tunnel.

"After it. No time to let it recover!"

Gandalf darted ahead. The tunnel was too tight for Smaug. Kael sent the dragon back the way they had come with the petrified Watcher in tow. Kael mounted Herpo instead, swept Gandalf up behind, and the basilisk surged forward, tongue tasting the trail. It needed no command. The demon's stink ran like a scar through the stone.

The underworld opened in a maze of veins. Tunnels ran in every direction, close and tight and then widening to caverns as big as cities. They seemed to thread the roots of the world.

Gandalf stared at them with a tension Kael had never seen.

"What is it? Something wrong with these tunnels?" Kael asked quietly.

Gandalf's voice dropped to a murmur, as if sound itself might wake what slept here. "May the Valar preserve us. Pray we do not meet what dwells in these depths. There are things here far more perilous than the Balrog."

Cold slid into Kael's chest. "What are they, to make you speak so?"

"I do not know their names. No one does. They are very ancient, nameless things. Even Sauron does not know them."

"I think the Balrog will avoid them. It knows these depths. Unless mad, it will not go where the nameless dwell."

The stone shivered under Herpo's glide as if the mountain had drawn a breath.

They caught the Balrog where the tunnel bent upward. The demon faltered, as if it had met something it feared more than death. From its sulfur-choked throat came a sound for the first time that was not a roar. It was high and short, almost a keening whimper, thin and raw with animal terror older than language.

It did not strike at them. It did not even look at them. It fled, climbing for a shaft that slanted upward.

Gandalf stiffened. He felt it too. "Go. Follow it. Do not look back."

Herpo tasted the air and sped on, bearing Kael and Gandalf in a desperate pursuit, as if some hunter followed behind that none of them dared see.

The earth began to tremble like a slow earthquake. Dust and slate sprinkled from the roof. Then a strange quiet fell. Not silence, but a swallowing of sound, as if thick curtains had smothered movement, breath, and heartbeat together.

A deeper darkness unfurled at the end of the passage. Not the absence of light, but a presence that erased it. A nothingness that was somehow there, a black that unmade color and line.

Whispering touched them. Not air to ear, but something brushing against the soul. It hummed with a cold, devouring hunger. It carried a malice too old to measure.

Terror bloomed in Kael, primal and wordless, like a serpent of ice coiling tight around his heart. He clenched his jaw, tightened his grip on the basilisk's plume, and kept his eyes fixed on the climbing Balrog ahead—anything but that widening, unnatural dark behind.