The iron door groaned open on ancient hinges, the sound reverberating down the stone stairwell like a funeral bell.
Light spilled from within—warm but subdued, the kind of light that did not chase away the shadows so much as learn to live among them.
And in that light stood a man.
Bent with age, his frame draped in simple gray robes.
His hair was thin and silver, his face lined with the passage of a century.
But his eyes—those piercing, eyes one blue one white—still burned with the same fire that once set half the world aflame.
Gellert Grindelwald.
For a heartbeat, the old man only looked at him.
Then his lips twisted into the faintest of smiles.
"Heh."
A low chuckle, gravelly from disuse.
"Took your time in finally getting here, boy."
Cassius blinked, confusion flashing across his face.
He opened his mouth to speak, but Grindelwald simply stepped aside, gesturing toward the chamber within.
"Come," the old man said. "The air is colder in the hall. Let us talk where the walls listen less."
Cassius hesitated only a moment before stepping across the threshold.
The chamber was spare but not barren.
A simple bed against one wall, a desk stacked with books and scrolls, shelves lined with instruments of silver and crystal that hummed faintly with restrained magic.
The windows, narrow and barred, allowed only a slice of the alpine sun.
It did not look like a prison so much as a hermit's sanctum, an exiles abode.
Grindelwald closed the iron door with a resonant thud, then shuffled to a chair near the desk.
His movements were slow but deliberate, each gesture carrying a weight of purpose.
Cassius stood in the center of the room, uncertain whether to bow or demand an explanation since he seemed to be expected.
The old man settled himself with a sigh, then fixed Cassius with that cutting stare.
"You're wondering what I meant," he said simply.
Cassius nodded.
Grindelwald's smile deepened, though it carried a bitter edge.
"Of course you are. You are clever. Clever enough to find me when others have forgotten I exist. Clever enough to wear the mask of a child and walk through gates where armies could not. But cleverness is not yet understanding."
The words struck Cassius like a scalpel.
He bristled but forced his expression to remain calm.
"Then explain it."
The old man leaned back, folding his hands over the knob of his staff.
His eyes drifted toward the barred window.
"My revolution," Grindelwald began, voice a low rumble, "was doomed before it began. I saw it too late. At first, I believed it was capable of succeeding to prevent the future my gift showed to me, but thanks to the meddling of Dumbledore and his flock of light-blinded fools that sealed my fate. And yes, they played their part. But the true enemy was time itself, the revolution needed to succeed during the initial uprising, only i was captured and imprisoned, this delayed the uprising after the period the muggles call the first world war, it was then that the revolution truly failed, for i was given a second vision, but it should have been taken as a warning not a sign, for by that time it was not dumbledore and his forces that were my greatest enemy but simply time itself."
Cassius tilted his head.
"Time?"
Grindelwald nodded.
"The tide of history. As the magical world fought between ideologies of remaining hidden or rising up behind my banner, the muggle word was equally being challenged, the first world war being a direct paralell conflict to our own wizarding revolution caused ripples in time that would cause the events of our inevitable downfall, weapons that magic could not contend with, but i saw it to late, and when i finally did get to witness the device used by the muggles to cease their war, i myself was left with nothing but a choice."
His gaze sharpened, like a blade unsheathed.
Cassius felt his breath catch, having already known what was coming.
"Nuclear fire," Grindelwald continued, voice dropping to a whisper. "A weapon to dwarf even Fiendfyre. A single detonation could wipe out a city, magic or no. Shielding charms were nothing in the face of this super weapon. Even powerful magical creatures like dragons were burned in the heat of that created inferno. That, boy, was the day the muggles eclipsed us. And it was the day I knew my revolution had failed."
Cassius' fists clenched at his sides.
The cold logic of it gnawed at him.
"So you surrendered," he said.
Grindelwald let out a humorless laugh.
"Not at first. My pride was not so easily broken. I fought, yes. But deep inside, I had already seen it."
"Seen what?" Cassius pressed.
The old man leaned forward, his eyes locking onto Cassius with unnerving intensity.
"You," Grindelwald said simply.
Cassius blinked, stunned.
"I am a Seer, boy. Not a charlatan, not a dreamer. I have glimpsed threads of what is yet to come. In the ashes of my defeat, two paths unfolded before me: fight to the bitter end and be erased entirely, or fall—publicly, gloriously—at the hands of Albus. Prison would be my penance… and my refuge. Until the one destined to finish what I began arrived."
Grindelwald's smile turned wistful.
"And here you stand. Decades later, but here nonetheless."
Cassius felt heat rise in his chest, a mixture of pride and unease.
"You mean… you waited... in exile for me?"
Grindelwald barked another laugh, shaking his head.
"Waited? Hah! Endured, boy. Forty years plus years I have sat in this stone cage, waiting for prophecy to take shape. Do you know what that does to a man? To know your moment has passed, yet your purpose is not yet fulfilled? It corrodes. It hollows. Yet… I endured."
His gaze softened, just slightly.
"Because I saw you. A child of shadows, cast out and forgotten. Clever, ruthless, yet capable of greatness. My heir. Not by blood, but by fire."
Cassius swallowed, mind racing.
The prophecy, one just like his twin had but with a far greater purpose.
The pieces clicked together in his head—the old man's surrender, his strange amusement, his welcome at the door.
It wasn't chance.
It was inevitability.
Still, skepticism edged his voice. "And you think I can succeed where you failed?"
Grindelwald's eyes gleamed.
"I know it. You are not bound by the world that shackled me. You have lived a life within the muggle realm, and already come to understand that with their technology they pose a risk to us wizards, and have no doubt been making moves already, moves that will bridge the gap, preparing the world for the big reveal, a reveal that cannot be stopped since by the time the others are made aware of your intentions it will already be to late."
Silence settled over the chamber.
Cassius stood rooted, heart hammering.
He had dreamed of allies, of teachers, of tools to hone his path of vengeance and revolution.
But this—this was something beyond even his designs.
A dark lord of legend, claiming him as his heir.
And yet… the fire in Grindelwald's eyes was not madness.
It was conviction, tempered by age, honed by loss.
Cassius drew a slow breath. "Then teach me."
The old man's smile widened, fierce and hungry despite the weight of years.
"Oh, I will, boy. I will. But first—"
He raised a gnarled finger.
"Understand this: my revolution was mine. Yours must be yours. You cannot inherit victory. You must forge it. I can give you wisdom, I can give you sight, but the blade must be your own."
Cassius nodded, resolve hardening.
Grindelwald leaned back, chuckling again.
"Good. Good. Then let us begin. Forty years I have waited to pass on the torch. Let us see if you can carry the flame."
A tapping sound from the window, brought cassius over to invite in his owl Noctis, before turning around to face his mentor.
"I will carry it," he whispered.
And in that moment, in the greatest prison the world had yet ever forged, a terrible twosome was forged.