As the Killing Curse struck, it hit the Balrog squarely.

The demon reeled as if grievously wounded, roaring in agony as the flames along its body guttered and flared erratically.

Panting and braced on his staff, Kael let a quick flash of relief cross his face.

It vanished an instant later. The Balrog shook off the basilisk's ocular magic, then snapped its flaming whip in fury. The blow swatted both the petrified "Watcher in the Water" and the ambushing basilisk aside, flinging them down into the black gulf.

Kael's heart lurched for Herpo, but there was no time. The Balrog loosed a low, uncanny bellow, and the surrounding fire streamed toward it as if swallowed by a furnace. The dimming blaze swelled anew. Heat hammered outward.

A flaming scepter formed in its hand. With a sweeping arc, a torrent of scorching fire blasted toward Kael and Gandalf.

Kael slammed his staff to the stone and poured in power. "Protego Maxima. Protego Totalum. Indestructible!"

A vast barrier rose and wrapped them both. The Balrog's heat climbed higher. Rock around them slumped and oozed, turning to magma. Even Kael's shield began to thin, as if the fire were melting the magic itself.

Worse, the fire-protection draught was fading. Pain pricked his skin again. He yanked fresh vials from his pocket, downed them hard, and thrust one to Gandalf.

"Drink. If the Balrog doesn't kill us, the heat will."

Gandalf tilted it back at once, then strode into the flame.

With Kael's Flammifer in hand, and Narya unveiled to its full strength, he shone with a fierce, consecrated fire.

"I am a servant of the Secret Fire, wielder of the Flame of Anor! The dark fire shall not avail you. No unclean thing can pass!"

Narya's hidden strength surged. Fire answered him like a tide. The Flammifer roared white and pure. Sacred blaze met demon fire, and the cavern became a sea of orange and white. Orcs too slow to flee vanished to ash. Pillars sagged and ran, the stone itself surrendering under the heat.

Kael took in the ruin and thanked every draught he had brewed. Without them, they would have cooked where they stood.

Gandalf held the line, forcing Narya and the holy fire to a wary stalemate. Kael snatched the Light of Eärendil from his belt, lifted his staff to the crystal, and whispered, "Lumos."

A simple charm, yet joined with the Star-glass it burst into cleansing brilliance. White light scoured the murk and stabbed at the Balrog's shadow. The fallen spirit recoiled with a hiss, beating its wings of darkness to shield its eyes.

Together they drove it back a pace. They both knew it would not last. Time favored only death unless they ended it now.

A dragon's roar rolled from the First Hall.

Kael and Gandalf brightened.

A heartbeat later, a mountain of bronze and scarlet broke the wall, armor clashing, wings carving the air as it dropped.

"Master, I'm here! The great Smaug comes to your rescue!"

"Save it for the bards. Help with the Balrog!" Kael snapped.

"Right. Watch this!"

Smaug's chest swelled. A river of dragonfire bathed the Balrog.

The demon stood and drank the flame as if it were air. Its heat swelled again.

Smaug's eyes widened. "Uh…"

Kael's face darkened. "Really? The Balrog is fire incarnate. Feeding it makes it stronger. Don't burn it—pin it!"

Chastened, Smaug lunged. A hundred meters of armored muscle slammed into six or seven meters of incandescent malice. Claws hammered. Fangs snapped. The tail smashed down like a falling tree. A dragon's body could buy time, and fire-drakes could endure heat longer than most.

But dragons are still flesh. The Balrog is a fallen Maia, living fire given will. Claw and fang could harry, not harm.

It was enough. The demon's lash cracked and wrapped Smaug's neck; the dragon bellowed, raked, tore free, and seized the Balrog in his jaws. The demon wrenched, whip snapping, scepter burning channels in Smaug's armor. The struggle slowed it and split its focus.

Pressure eased on Kael and Gandalf.

Then at last, the familiar chime rang in Kael's mind.

[Hogwarts Check-in System: Location—Moria. Check in?]

"Check in," he thought, eyes flaring.

[Success. Reward: Grindelwald's modified Fiendfyre.]

Understanding flooded him. Fiendfyre devoured all. Only a madman or a master would cast it indoors. Grindelwald had been both, and more; he had taught the fire to spare its allies.

Kael slashed the air. Eerie blue fire tore from his wand, heatless to friend, ravenous to foe. It ate the Balrog's flame and rose in the shape of a blue-fire Balrog to meet it.

Gandalf recoiled, then felt no heat from the azure tide and steadied. The Balrog snarled, eyes snapping to the mockery that challenged its dominion.

At Kael's will, the blue demon charged. Whip met whip. Scepter met blazing fist. Blue and orange detonated, shock hitting like a giant's drum. The hall became a furnace within a furnace.

The true Balrog writhed and ripped the fire-construct apart, tearing the Fiendfyre shape to embers. The blue tide fell back to a raging sea, still devouring, but no longer contending blade to blade.

Not enough. Kael's thoughts leapt to another memory. In the old fate, Gandalf and the Balrog fell into the depths. Water drowned the demon's flame.

Not the water he had conjured earlier, which boiled away at once. Deep water. Ulmo's grasp.

"Gandalf. What water can quench a Balrog?"

Gandalf blinked, then his eyes sharpened. "Ulmo is Lord of Waters. All rivers are his. He hates the servants of Morgoth. In water they are shackled. Draw it into water, and its flame will fail."

They looked to the abyss. Heat haze shimmered, but a breath of cool touched Kael's cheek.

"Vapor," Gandalf said softly. "There is water below."

How to send it down?

Smaug reeled. His armor flowed like wax where the scepter kissed it; scales glowed cherry-red. The dragon howled. Fire-drakes resist flame, but the dark fire of Udûn is more than flame.

Your foe is me, servant of Morgoth.

Gandalf stepped to the center of the bridge. The Flammifer blazed, its light pure as sunrise. The Balrog's gaze fixed on him. It stepped onto the span.

The whip flicked. The lash hissed through the air for Gandalf's throat. Air ignited in its wake, the heat scarring the stone.

Gandalf twisted aside and met it, sword to lash. Thunder shook the bridge. The shock cracked the arch; dust sifted down into the gulf.

He staggered. The blade's light dimmed and flared again.

The Balrog pressed forward, eyes mocking.

"Avada Kedavra!" Kael struck from the flank.

The demon snapped the whip into the curse. The lash shattered. The green lightning died.

"Now," Gandalf breathed.

He drove his staff into the keystone. Stone boomed. The arch split. The span fell away in a roar, blocks crashing into the dark.

The rock beneath the Balrog vanished. With a bellow that shook the halls of Khazad-dûm, the demon dropped.

A flaming lash flashed up, curling for Gandalf's leg.

"Protego!" Kael's shield caught it and flung it wide.

The whip snapped out again, caught a jag of rock on the far wall, and held. The Balrog heaved, climbing the cliff like a spider of fire.

Kael tore Aeglos free and rammed the spear into the wall. Power shuddered down its length into the stone.

Cracks raced like lightning. Ledges sheared. What remained of the arch and a swath of wall tore free. Rock, fire, and fury fell together, dragging the climbing Balrog down into the chasm and toward whatever water waited in the dark.