The first major breakthrough in Hermione's investigation came from Harry's frustration, which was fitting in a way she only appreciated afterward.
Harry had been pacing behind a row of chairs in the common room for several minutes before the sentence finally came out. It was late enough that the room had thinned to clusters of tired conversation and half-finished homework, the fire low, the shadows in the corners softening the edges of everything. Hermione sat with parchment spread across her knees and several books open around her, though she had long since stopped pretending the books were the primary reason she remained there. Ron lounged nearby in the posture of someone who wished to seem detached from a conversation he had no intention of actually missing.
"He always does it right before people change," Harry said.
Hermione looked up sharply. "That's not true."
The objection came automatically, and because it came automatically, it told her she had heard something important.
Harry stopped pacing. "It is."
"No," she said again, but more slowly this time, because she was already searching her own notes and memory with the peculiar internal speed that made her silences feel crowded. She began checking examples almost instantly. Neville after Charms. The Hufflepuff before the library incident. The Ravenclaw whose posture had changed over a week of tiny interventions. The Gryffindor in the study room. Theodore under pressure. Even Harry himself in their conversations—Tom did not move first. He waited.
Hermione bent over the parchment and started writing.
Not before weakness.
At threshold.
Harry came around the chair to look over her shoulder. "What?"
She barely glanced up. "You're half-right."
"That's comforting."
"No, listen." She set down the quill, then picked it up again almost immediately because thinking without an object in hand made her feel wasteful. "He doesn't create the first crack."
Harry went still.
That was it.
That was the constant.
The realization moved through Hermione with a clarity so sharp it was almost physical. Tom did not build people's vulnerabilities from nothing. He did not manufacture weakness wholesale. He did not approach stable students at random and impose new structures over them by force of brilliance or presence. He waited. He watched until some internal threshold had already been approached—humiliation, self-consciousness, frustration, overcompensation, uncertainty, exhausted accommodation, moral overcommitment—and then he intervened at exactly the point where his words would feel less like influence and more like recognition.
"That's why people don't resist him," Harry said.
"Yes," Hermione replied. "Because by the time he says something, it already feels true."
The simplicity of the principle made everything else worse.
For weeks Hermione had been recording effects, tracking wording, timing interactions, studying the distributed consequences of what Tom said and withheld. She had known he selected for response. She had known he diagnosed rather than advised, at least in many cases. She had known he preferred moments of instability. But this was cleaner. This was the governing pattern beneath the others.
He waited for internal readiness.
Not readiness in the positive sense—not openness, not willingness, not anything as kind as that. Readiness in the structural sense. The moment at which a person had already begun to bend and therefore could be shaped with less visible force.
Harry understood the implications quickly, perhaps more quickly than he realized he could. "That means if he says the same thing too early, it wouldn't work."
Hermione looked at him with something very close to startled approval. "Exactly."
That, too, mattered. Method had limits. If Tom required threshold states, then he was not omnipotent in the childish sense. He could not simply rearrange anyone at will. He depended on timing, on observation, on the existence of pre-existing fault lines. Every method, however elegant, contained within it a boundary.
Hermione wrote again.
Waits for internal readiness.
Intervention must arrive after instability begins, before it resolves independently.
For the first time since they began this, she felt something close to real alarm—not the scattered unease that had motivated the list, nor even the analytic dread that came with accumulating evidence, but a colder fear shaped by elegance. Crude methods could be stopped crudely. A boy who yelled, threatened, or hexed others in corridors could be watched, punished, isolated. Tom's method was beautiful in the worst possible sense. It used existing motion. It wasted little. It let people experience the intervention as self-discovery or necessary truth rather than external control.
Elegant things, Hermione thought, were always harder to interrupt without understanding them completely.
Harry, still standing over her shoulder, seemed to be replaying his own history with Tom under the new frame. Hermione could almost see the retrospective adjustment occurring in him.
"He did that to me," Harry said.
She looked up. "Yes."
"No, I mean—he waited." Harry's voice had gone quieter, not weaker but more exact. "In those conversations. He never just started on me. He waited until I'd already decided something. Then he shifted it."
Hermione nodded slowly. She had been suspecting as much, but hearing Harry say it in those terms confirmed something else: Tom's threshold-reading was not limited to embarrassment or insecurity. It extended to moral pressure too. With Harry, the threshold was often reached when moral certainty tightened into urgency. Tom waited until Harry had committed inwardly to a frame of right and wrong, then moved the ground beneath the frame itself.
"That's why it feels destabilizing afterward," Hermione said. "He doesn't argue you away from yourself. He changes the terms while you're standing on them."
Ron, who had been following more of this than either of them probably realized, let out a low breath. "Brilliant. So he waits until people are already wobbling and then tells them which way they're falling."
Hermione turned toward him.
The phrasing was rougher than hers would have been.
But correct enough.
"Yes," she said.
Ron made a face as though he disliked being right about something this unpleasant.
The breakthrough changed their work almost immediately. Observation without threshold had been broad. Now it could be narrowed. Hermione restructured her notes that very night, dividing examples not merely by person and context but by precursor state. Public embarrassment. Private frustration. Repeated self-doubt. Social overextension. Moral certainty. She began marking not just when Tom spoke, but what emotional or cognitive condition had stabilized just beforehand.
Harry, once given the pattern, grew sharper too. He had always been better than Hermione at reading when another student was near some internal edge, even if he lacked her language for categories. Now that edge itself became a thing to watch. In meals, corridors, and courtyards, he started noticing moments he might once have felt only as atmosphere: the pause before anger hardened, the look of someone trying too hard not to seem upset, the thin false-laugh students used just before pride turned brittle.
Tom, he realized, had been living in those moments all term.
That thought kept returning.
Not lurking, exactly. Not hovering like a predator in the childish sense. Something subtler and worse. Tom watched for the human instant at which resistance became porous—not collapsed, simply porous enough that the right sentence would enter as truth instead of pressure.
Hermione saw that realization darken Harry's face and knew she had reached something dangerous in him. Not because he would do something stupid immediately—he had grown out of some of that, painfully—but because understanding method this clearly made Tom's actions seem both more comprehensible and more invasive. Harry preferred visible wrongness. Threshold manipulation was harder to hate cleanly because it so often attached itself to realities the victim had already begun to feel.
That made it harder to fight without also contesting someone's self-understanding.
The following day in class, Hermione tested the insight silently. She watched a Ravenclaw boy grow increasingly frustrated during a practical exercise, missing not because he lacked ability but because his embarrassment at earlier hesitation had made him too self-conscious to trust his own movement. Tom noticed him. Of course he did. But Tom did not move immediately. He let the frustration concentrate. He let the boy's face settle into that particular tightness Hermione had now come to recognize—not pure confusion, not open shame, but readiness for someone else to name what was wrong.
Only then did Tom step near enough to speak.
Hermione could not hear the words from where she sat. She did not need to. The timing alone confirmed the structure.
Her pulse rose with something close to triumph and dread mixed together.
She was right.
Which meant Tom's method was real in the strongest possible sense—not merely a pattern they had projected onto him, but a repeatable structure that could be anticipated.
That should have been comforting.
It was not.
Because a repeatable structure is also a teachable one.
That night, lying in bed while the dormitory settled around her, Hermione replayed the discovery until it ceased feeling like a fresh conclusion and became a grim new baseline instead. At threshold. Not before weakness. At threshold. The phrase repeated in her head with the same clean force some equations had once carried. She understood now why Tom's influence spread so efficiently while remaining deniable. Most people interpreted intervention through content alone. They asked what had been said and whether it was fair, accurate, helpful, cruel. They paid less attention to the precise state into which the sentence had been delivered.
Tom paid almost exclusive attention to that.
For the first time, Hermione saw clearly why adults were so slow to recognize the danger. Adults heard content and saw outcomes. Tom worked in timing.
And timing, unless one was already watching for it, vanished almost as soon as it occurred.