The expulsion of the mutinous members from Dumbledore's Army did not quell their sense of entitlement; it festered into a bitter, indignant rage. Zacharias Smith, in particular, could not stand the public humiliation. He began to whisper in the corridors, trying to build a new narrative: that Harry and his "elite" friends were hoarding knowledge, that Ariana Dumbledore was an arrogant snob who thought she was too good to help ordinary students.
Ariana, of course, was aware of this campaign. She classified it as "post-rejection emotional vocalization" and paid it no mind. It was irrelevant data.
The confrontation she knew was logically inevitable came a few days later.
She was walking alone down a deserted corridor on the fifth floor, heading towards the library. It was a calculated risk; she knew she was being observed, but she also knew the limits of her opponents' courage. They would not dare to act in a crowded hallway.
As she rounded a corner, she found her path blocked. Zacharias Smith stood there, flanked by Marietta Edgecombe and the four other students who had walked out of the D.A. They had positioned themselves in a loose, intimidating semi-circle. Their wands were out, though held uncertainly.
"We want to talk to you, Dumbledore," Zacharias sneered, trying to sound brave but failing to conceal the nervous tremor in his voice.
Ariana stopped, her expression one of mild, academic curiosity. She did not reach for her wand. She simply waited. She could feel another presence around the corner, a familiar, powerful magical signature, hidden and observing. Professor McGonagall. As she had anticipated, her Head of House was keeping a discreet, protective eye on the situation. This changed the variables from a potential threat to a controlled experiment.
"You have my attention," Ariana said, her voice calm. "Though I estimate the value of this conversation will be minimal."
"We're not leaving until you agree to teach us," Marietta chimed in, her voice shrill. "It's not fair that you only help Potter and your special friends. We have a right to learn proper Defence too!"
"You have a right to the education provided by this institution," Ariana corrected gently. "An education which you are all receiving from Professor Stump. Any supplementary instruction is a privilege, not a right. A privilege you forfeited when you demonstrated a lack of loyalty and commitment."
"We're not taking no for an answer!" Zacharias blustered, growing bolder. He and the others raised their wands, pointing them directly at her. "You're going to teach us, or we'll make you."
The air crackled with a pathetic, unfocused magical intent. Six wands against one unarmed girl. The odds, to any casual observer, would have seemed overwhelming.
Ariana's expression did not change, but a flicker of something—not fear, but a profound, weary disappointment—passed through her eyes. "You are threatening a fellow student? An Order of Merlin recipient? In a Hogwarts corridor? Your grasp of strategy is as poor as your grasp of ethics."
She sighed, a soft, exasperated sound. "Very well. You wish for a demonstration."
She looked at their six raised wands. "Do your worst."
It was a direct challenge, an insult to their collective power that they could not ignore. Spurred on by a mixture of rage and wounded pride, Zacharias yelled, "Get her! Stupefy!"
The others followed suit. "Impedimenta!" "Petrificus Totalus!"
Six different spells, six jets of coloured light, shot from their wands simultaneously, converging on the single, motionless point where Ariana stood.
She didn't move. She didn't draw her wand.
She simply snapped her fingers.
The sound was soft, almost delicate, but the effect was absolute. In the instant before the spells could reach her, a dome of pure, crystalline, silver light erupted around her. It was not the shimmering, translucent shield of a Protego. It was a solid, flawless, and utterly silent barrier of pure, condensed will.
The six spells slammed into the dome at the same time. The impact was completely negated. There was no explosion, no flash of light, no sound of magical collision. The curses simply… vanished. They were not blocked; they were unmade, their magical energy absorbed and dissipated by the shield as if it were a drop of rain hitting the ocean.
The six students stared, their mouths agape, their wands held limply. They had thrown their combined magical strength at her, and she had defeated it with a snap of her fingers.
"As I suspected," Ariana's voice came from within the dome, calm and laced with a faint, academic mockery. "Your collective power output is statistically insignificant. You failed to synchronize your casting, your spell choices were contradictory, and your intent was unfocused. A truly pathetic display."
Before the humiliated students could even process the insult, another, far more terrifying presence made itself known.
"That is quite enough."
Professor McGonagall strode around the corner, her face a mask of cold, righteous fury. Her wand was out, and with a series of sharp, whip-like motions, she disarmed all six students, their wands flying from their hands and into her own.
"Pointing your wands at a fellow student," she said, her voice dangerously quiet, which was far worse than shouting. "Threatening her. Casting spells with intent to harm. Six of you against one." Her eyes, burning with a lioness's protective fire, swept over them. "A month's detention. Each. With Mr. Filch. And I will be sending an owl to each of your parents this evening, detailing this disgusting, cowardly behavior. You are a disgrace to your houses, and to this school."
She then looked at Ariana, who calmly let her shield dissolve with another, silent snap of her fingers. McGonagall's stern expression softened with a flicker of profound relief and respect.
Ariana simply looked at the six trembling, terrified students. She shook her head slowly, a gesture of pure, intellectual disappointment.
"And you didn't even manage to scratch the shield," she said, her voice a final, quiet, devastating verdict. "Pathetic."
With that, she turned and continued her walk towards the library, leaving her would-be assailants to face the full, terrifying wrath of her Head of House. The experiment was concluded. The data was clear. And the lesson, she hoped, had been permanently learned.