The start-of-term feast at Hogwarts was abuzz with an energy that went beyond the usual reunion excitement. Dumbledore, his eyes twinkling with a particular brand of theatrical gravitas, had made two stunning announcements.
First, the Inter-House Quidditch Cup was cancelled for the year. This was met with a roar of outrage and disappointment from the students, particularly the Quidditch players.
Second, he announced the reason: Hogwarts would be hosting the Triwizard Tournament, a legendary magical competition between the three largest European schools of witchcraft and wizardry—Hogwarts, Beauxbatons Academy of Magic, and Durmstrang Institute. He explained the history, the glory, and the unfortunate fatality rate that had led to its discontinuation centuries ago. He assured them that new safety measures were in place, and that an age line would be drawn to prevent any student under the age of seventeen from entering.
The hall erupted in a feverish babble of excitement, the loss of Quidditch instantly forgotten in the face of this new, thrilling prospect.
Then, Dumbledore made his final introduction. "We also have a new addition to our staff this year," he announced. "Please join me in welcoming our new Defence Against the Dark Arts teacher, Professor Alastor Moody."
The great oak doors of the hall swung open. A man stood there who seemed to be carved from ancient, battle-scarred wood. He limped heavily on a clawed, wooden leg, and his face was a roadmap of old scars. One of his eyes was small, dark, and normal. The other was a large, round, electric-blue orb that whizzed and spun in its socket, completely independent of his normal eye, scanning the hall with a disturbing, penetrating gaze. A palpable aura of paranoia and battlehardened power rolled off him in waves. This was Mad-Eye Moody, the most famous Auror of his generation.
The students stared, a mixture of fear and awe on their faces.
As Moody limped into the hall, Ariana heightened magical senses, honed by a summer of intense research and her own maturation, registered a profound and immediate dissonance. She saw the man—the scars, the magical eye, the aura of power. But beneath it, like a discordant note in a symphony, she felt something else.
It was the sense of knowledge that Polyjuice Potion was currently being used.
She had studied its complex alchemical properties with the Flamels. She knew its feel, the way it imperfectly masked the user's core magical essence, leaving behind a faint residue that only the most sensitive of magical beings could detect. To her, the man who called himself Alastor Moody was like a lie.
Her mind, with its terrifying speed, immediately knew the dots. The Triwizard Tournament at Hogwarts. A supposedly trusted new professor. A complex, year-long plan. And Harry Potter, the boy Voldemort was obsessed with. This was Barty Crouch Jr., the supposedly dead Death Eater playing the game of teacher.
A cold, calm certainty settled over her. This was not a threat to be monitored. This was a threat to be neutralized. Immediately.
She would not wait for a champion to be chosen. She would not wait for mysterious clues and dangerous tasks. She would not allow the charade to continue for a single day longer than necessary.
That evening, after the feast, while her friends were excitedly discussing the Tournament, Ariana slipped away and sent a Patronus message to Dumbledore's office, requesting a private and urgent meeting on a matter of "critical internal security."
She was summoned at once. She entered the familiar circular office, where Dumbledore sat behind his desk, looking at her with a curious, expectant expression.
"Ariana," he said warmly. "A pressing matter so early in the term?"
"Professor," she began, her voice low and serious. "The man you have hired as the Defence Against the Dark Arts teacher is an imposter."
The twinkle in Dumbledore's eyes vanished, replaced by an expression of profound, sharp attention. He did not question her. He did not doubt her. He had learned over the past year that when Ariana Dumbledore made a definitive statement, it was based on data, not on speculation.
"Explain," he said simply.
"He is using a continuous dose of Polyjuice Potion," she stated. "My senses can detect the residual magical signature. It is faint, but unmistakable. The man in that hall is not Alastor Moody." She paused. "Given the timing of his arrival with the Triwizard Tournament, and the overarching threat to Harry Potter, the logical conclusion is that he is a servant of Lord Voldemort, placed here to manipulate the Tournament for his master's ends."
Dumbledore listened, his face becoming a grim, stony mask. He had had his own subtle suspicions, a faint unease he couldn't quite place. Ariana had just given it a name and a terrifyingly plausible identity.
"Your senses are… remarkable, my dear," he said, his voice grave. "I fear you are correct." He looked at her, his mind clearly working through the ramifications. "To confront him directly would be dangerous. If he is who you suspect, he is a powerful and desperate wizard."
"A direct confrontation is unnecessary and tactically unwise," Ariana countered smoothly, already two steps ahead. "A public accusation would cause mass panic and a Ministry investigation that would compromise the school. We require a controlled environment. A trap."
She laid out her plan with the cool, efficient logic of a master strategist.
"You will call a mandatory, emergency staff meeting tomorrow morning," she instructed. "Inform them it is a security briefing regarding the Tournament, delivered by Professor Moody himself. It is a plausible reason that will not arouse his suspicion. The meeting will take place in the faculty lounge."
She continued, her voice precise. "Before the meeting, you will contact Amelia Bones. You will inform her that you have credible intelligence of an infiltrated Death Eater operating within the castle. You will request a small, elite team of Aurors, including Kingsley Shacklebolt and Nymphadora Tonks, to be present. They will be hidden, Disillusioned, and waiting in the antechambers of the lounge."
Dumbledore nodded, his expression one of intense focus.
"When the staff is assembled," Ariana concluded, "you will ask Professor Moody to demonstrate a security charm. As he raises his wand, you will give the signal. The Aurors will emerge. He will be surrounded, outnumbered, and with no avenue of escape. We will not give him a chance to fight. We will simply… apprehend him. The entire affair will be over before the rest of the school has even finished breakfast."
The plan was perfect. It was a silent coup, a trap so elegant and absolute that the target would not even know he was in danger until it was too late. It used the imposter's own cover story against him and leveraged the full authority of both the school and the Ministry to ensure a swift, bloodless resolution.
Dumbledore looked at the fourteen-year-old girl standing before him, and for a moment, he felt a profound sense of awe. He had spent decades playing a long, complex game of chess against Voldemort. Ariana had just looked at the board, identified the enemy's most powerful piece, and devised a plan to take it off the board on the second move.
"An impeccable strategy, Ariana," he said, his voice full of a deep, almost weary respect. "I will make the arrangements at once." He stood up, a new, hard light in his eyes. "It seems Professor Moody's tenure at Hogwarts is going to be even shorter than we anticipated."