Purple lightning struck first.
The First Sentinel brought its massive arm down, and a bolt of violet energy exploded across the chamber floor. Stone shattered like glass, sending shards skidding across the cavern.
"Scatter!" Rovan shouted.
The group split apart as the blast tore through the space where they had been standing seconds before.
Aeralyn rolled across the ground and came up on one knee. Golden warmth flared in her palms as she raised her hands toward the towering guardian.
A burst of radiant fire surged forward.
The blast struck the Sentinel's chest.
But instead of shattering its armor, the golden light slid across the dark crystal plates like sunlight across frozen glass.
The First Sentinel barely moved.
"…That's not good," Teren said from behind a broken pillar.
Caelum stepped forward, frost swirling around his arms like storm clouds.
"This one was not built like the others."
"No kidding," Rovan muttered.
The giant took another step.
The chamber shook.
Behind it, the Core Engine continued turning, streams of golden and blue magic spiraling between its ancient rings as the Heart of Balance hovered at its center.
The Heart pulsed faster.
Reacting.
Responding.
Aeralyn could feel it pulling at her magic again.
Like it wanted something from her.
"Aeralyn!" Lysa called.
The First Sentinel raised its arm again.
But this time it wasn't aiming at the Heart.
It was aiming at Caelum.
The violet rune on the Sentinel's chest flared brighter.
A beam of dark energy shot across the chamber.
Caelum raised both hands.
A wall of ice erupted in front of him.
The beam slammed into it.
The barrier shattered instantly.
Caelum was thrown backward across the chamber floor.
"Caelum!" Aeralyn cried.
The prince slid across the stone and crashed against a fallen piece of crystal.
He forced himself up, breathing hard.
"It recognizes royal winter magic," he said grimly.
"It sees me as a rival command source."
Teren blinked.
"So the giant ancient war machine thinks you're trying to steal control."
"Yes."
"That seems like a problem."
The Sentinel stepped forward again.
Purple energy crackled along its arms.
Aeralyn felt the Heart surge suddenly.
Warm power rushed through her chest like rising fire.
She looked up.
The Heart of Balance was glowing brighter than ever.
The golden beam between the Heart and the Core Engine thickened.
Caelum's eyes widened slightly.
"The Heart is trying to merge the two powers."
"Merge what?" Rovan asked.
"Warmth… and winter."
Another tremor shook the chamber.
Outside, the golden Sentinel guarding the entrance slammed into two of the advancing blue Sentinels, holding them back from the cavern.
But the First Sentinel inside was far stronger.
It lifted its arm again.
Energy gathered for another devastating strike.
Aeralyn stepped forward.
"No."
Everyone looked at her.
Golden fire swirled around her like living sunlight.
The Heart pulsed again.
She could feel it now.
Not just warmth.
Balance.
Winter and warmth flowing together like two halves of the same power.
She looked at Caelum.
"Your magic," she said.
"And mine."
Caelum understood immediately.
"You mean to combine them."
"Yes."
Teren stared at them.
"Is that safe?"
Rovan shrugged.
"At this point, who cares?"
The First Sentinel unleashed another beam.
This one larger.
More powerful.
Caelum stepped beside Aeralyn.
Cold energy spiraled from his hands.
Aeralyn raised hers.
Golden light surged outward.
The two forces met in the air.
Warmth and winter collided—
Then fused.
A massive wave of silver light burst forward.
The combined magic slammed into the First Sentinel's chest.
The violet rune cracked.
A deep fracture spread across the ancient symbol.
The giant staggered for the first time.
Rovan grinned.
"Now we're getting somewhere!"
Lysa fired an arrow straight into the cracked rune.
The impact widened the fracture.
Purple energy leaked from the break like escaping lightning.
The Sentinel roared.
It lifted both arms for one final strike.
But the Core Engine flared brightly behind them.
The Heart of Balance pulsed like a rising sun.
Aeralyn and Caelum stood together.
Warmth and winter spiraled around them as one.
Aeralyn took a deep breath.
"Again."
Caelum nodded.
They raised their hands together.
The chamber filled with blinding silver light.
And the final clash between balance and the ancient guardian began.