The Hogwarts Express rattled through the Scottish countryside, the familiar rhythm a comforting backdrop to the lively chatter within the compartment. Their expanded group had managed to secure a large carriage to themselves. Harry, Ron, and Hermione were catching up on their respective summers, while Daphne and Tracey were engaged in a quiet but intense game of wizard's chess. Ariana sat by the window, a book of advanced Arithmancy open but unread in her lap, her senses attuned not to the pages, but to the subtle shifts in the magical atmosphere around them.
As the afternoon wore on and the sky outside grew dark with a sudden, unseasonable storm, a strange and creeping cold began to seep into the carriage. It was a cold that had nothing to do with the weather. It was a deep, penetrating chill that leached the warmth from the air and seemed to settle in the very marrow of their bones. The cheerful chatter faltered and died. The windows frosted over, not with natural condensation, but with a creeping, feathery ice.
Ron rubbed his arms, shivering. "What's going on? Has the heating broken?"
Hermione looked around, her face pale with a sudden, inexplicable dread. "I… I feel awful. So… sad."
Harry felt it worst of all. A wave of bone-deep misery washed over him, a feeling of utter despair, as if all the happiness in the world had been extinguished. Faintly, at the edge of his hearing, he could hear a high, pleading scream. His mother's.
But Ariana was already moving. The moment the unnatural cold had touched the edges of her perception, her mind had identified the threat. Dementors. The guards of Azkaban, searching the train for the escaped Sirius Black.
"Stay here," she commanded, her voice cutting through the fog of misery that was descending upon them. She stood up, her posture serene but her eyes holding the cold, hard light of a winter star. She drew her Elder wand.
The train jolted to a sudden, screeching halt, throwing them forward in their seats. The lights flickered and died, plunging the carriage into a near-total darkness, broken only by the faint, eerie glow from the frosted windows. A slow, shuffling, dragging sound began to echo from the corridor outside.
A profound terror seized the other students. Ron was white-faced, trembling. Hermione had her arms wrapped around herself, tears of unexplained sadness welling in her eyes.
Harry was slumped in his seat, his face ashen, his hand clamped to his scar as the ghostly screams grew louder in his mind.
"Expecto Patronum."
The words were spoken by Ariana, not as a desperate shout, but as a calm, unwavering command. Her voice was the only clear, strong thing in the suffocating silence. A brilliant, blinding silver-white light exploded from the tip of her wand, a light so pure and powerful it was like a shard of a newborn star. It was not a misty shield; it was a corporeal, incandescent being.
The light took the form of a magnificent Thunderbird.
It was a creature of immense size and majestic power, its body formed of shimmering, solidified light, its great wingspan easily filling the corridor outside their compartment.
Its eyes were blazing sapphires, and crackling tendrils of pure, positive energy, like miniature lightning bolts, danced along its feathers. It let out a silent, piercing cry that was not a sound, but a wave of pure, unadulterated joy and hope that washed through the carriage, pushing back the encroaching despair.
Just as the shadowy, cloaked hand of a Dementor slid the compartment door open, the
Thunderbird struck. It didn't wait for the Dementor to enter. It surged forward, slamming into the dark creature with the force of a magical battering ram. The Dementor was thrown backwards down the corridor, its foul presence repelled by the overwhelming force of pure, positive energy.
Ariana didn't stop there. She stepped out of the compartment and into the darkened corridor, her stance firm, her wand held steady. The spectral Thunderbird wheeled in the narrow space, its incandescent light casting long, dancing shadows. It became a sentinel, a living wall of light that patrolled the length of their carriage, preventing any of the other Dementors from approaching.
The other students, peering from their own compartments, saw only a blinding, beautiful light and the shadowy forms of the dark guards of Azkaban recoiling from it.
The despair receded, driven back by the Patronus's powerful aura. Inside the compartment, Harry's breathing steadied, the ghostly screams fading from his mind. Hermione and the others looked up, their fear replaced by utter, staggering awe.
The standoff lasted for what felt like an eternity. Ariana stood her ground, a lone, serene figure holding back the tide of darkness, her concentration absolute, her Patronus an unwavering beacon.
Finally, a new light appeared at the far end of the corridor. It was the warmer, gentler light of a different wand. A man in shabby, patched robes was making his way down the train, his face kind but etched with weariness. It was Remus Lupin, the new Defence Against the Dark Arts teacher. He saw the scene—the terrified students, the last of the retreating Dementors, and the magnificent, crackling Thunderbird standing guard before a single, calm third-year girl. His eyebrows shot up in profound astonishment. He had been expecting to find panicked children, not a full-fledged, corporeal Patronus holding a dozen Dementors at bay.
As he approached, the Thunderbird, sensing the primary threat was gone, turned its sapphire eyes to Ariana. It dipped its great, shining head in a gesture of acknowledgement before dissolving into a shower of silver sparks, returning to the tip of her wand.
Lupin stopped in front of her, his gaze sweeping from her calm, composed face to the awe-struck students in the compartment behind her.
"That," he said, his voice full of a deep, incredulous respect, "was a Patronus Charm of a power I have not seen since Albus Dumbledore himself. May I ask your name?"
"Ariana Dumbledore," she replied, her voice steady, though a faint weariness now touched the corners of her eyes. The charm had required a significant expenditure of emotional and magical energy.
Lupin's eyes widened slightly at the name. Of course. It would have to be a Dumbledore.
He offered her a piece of chocolate from a bar he produced from his pocket. "Here. You'll need it. The Dementors affect us all, but a Patronus Charm of that magnitude takes a heavy toll."
She accepted it with a grateful nod.
He then turned his attention to Harry, who was still looking pale and shaken. "Are you alright, son?" he asked kindly.
"I'm fine," Harry mumbled, embarrassed by his reaction.
Lupin gave him a piece of chocolate as well. "Eat. It will help." He looked around at the students, his expression grave. "The Dementors are searching the train for Sirius Black. It seems they are not overly concerned with discretion." He sighed, a sound of deep, old weariness. "An apology will be made by the Ministry, I'm sure. But the damage is done."
He looked at Ariana one last time, a new, profound respect in his eyes. He had come onto this train expecting to be the sole protector of its students. The year had barely begun, and already, it was clear that this quiet, serene girl was a force to be reckoned with, a sentinel of light against the encroaching darkness