After exchanging a few brief words with Alastor Moody who was, in truth, Barty Crouch Jr. in disguise Sherlock felt his earlier suspicions solidify into certainty.
Simply put, running into Moody at this time and place, and walking up to greet him, was the most natural thing they could have done. Spinning around and leaving, or ducking into hiding the moment they spotted him, that would have looked deeply suspicious. That was the sort of thing Neville would have done.
Sure enough, once their exchange was over, the man did exactly as Sherlock had anticipated: he began questioning them about their purpose here.
Sherlock didn't so much as blink.
"We have something we'd like to ask Professor Lupin," he said.
"Lupin?"
Barty Jr. followed Sherlock's gaze toward the Defense Against the Dark Arts office not far down the corridor. A moment later, his face hardened, his tone turning grave.
"Holmes, I trust you're aware of the rules of the Tournament."
"Yes, I am."
"Professors are strictly forbidden from assisting contestants in their preparation for the tasks. That prohibition is clear-cut."
Watching the man commit so fully to the performance, Sherlock matched him beat for beat.
"I think you've misunderstood, Mr. Moody. We're not here about the Triwizard Tournament."
"Then what is it? As a member of the panel of judges, I have every right to ask."
"It's a personal matter concerning Gemma."
"Concerning Miss Farley?"
Barty Jr. turned to look at Gemma, both his natural eye and his magical one spinning toward her at once.
"That's right." Gemma nodded immediately, backing him up without missing a beat.
Her expression was perfectly composed, not a trace of guilt.
"Very well. Go ahead, then. Though I'll be having a word with Lupin afterward to confirm your story."
His gaze swept over their tightly clasped hands, and that ghastly smile, more pained than cheerful returned to his face.
"And Holmes—best of luck to you, Potter, and Diggory in the third task."
Without waiting for a response, he turned away, thumping his walking staff against the stone floor as he limped off.
"Ah, to be young," he muttered. "A world of possibilities."
His words and the rhythmic thud, thud of his wooden leg echoed together down the empty corridor, growing fainter, then fainter still, until both sounds disappeared around the corner.
Only when that hunched silhouette had fully vanished from sight did Gemma let out a long, trembling breath. Her palm was slick with sweat.
Sherlock had already explained the Marauder's Map to her, how to read it properly. So when she had followed him into the castle and seen the name Barty Crouch marked on the parchment, yet watched Alastor Moody standing in that very spot, she had understood at once how serious this was.
The man they had just spoken to was not the real Moody at all. It was Barty Crouch, wearing his face.
What she couldn't fathom was why a retired Head of the Department of Magical Law Enforcement would go to such lengths infiltrating Hogwarts in another man's skin. Was it restlessness? A hunger to reclaim some lost power? Or was it something far worse?
Whatever the reason, a conspiracy of enormous proportions lay hidden beneath the surface.
And Sherlock, it seemed, had already brushed up against its very core.
"I can tell you're frightened," Sherlock said quietly.
His voice pulled her back.
"Yes," Gemma admitted, without trying to hide it.
Even now, having reacted on instinct the moment she realized what Sherlock was doing and fallen seamlessly into step beside him, even now, looking back on it made her heart clench.
Sherlock gave a small smile and took her hand, leading her forward. When he felt how damp her palm was, he added:
"You did brilliantly, Gemma."
When she realized Sherlock was leading her in the direction of the Defense Against the Dark Arts office and not somewhere else entirely, Gemma blinked in surprise. She had assumed his story about visiting Lupin had been nothing more than a convenient lie to satisfy Moody.
As if he had read her thoughts, Sherlock paused at the office door.
"I've told you before," he said, his tone even, "that I don't lie, not unless it's necessary."
Then he raised his hand and knocked.
Gemma stared at him. '…Right.'
The door opened promptly.
Sherlock and Gemma found Lupin in the act of tucking his wand away. He looked up and the surprise that flickered across his face was immediate and unmistakable.
He had expected Harry at this hour. After all, he'd just finished coaching the boy and made his position clear; Harry coming to see him would have been the natural next step.
Sherlock's arrival, too, he had anticipated. Given how much Harry trusted him, Harry would certainly have told Sherlock everything about the afternoon's session.
But Gemma Farley, a student who had graduated the last year appearing alongside them? That, he had not foreseen at all.
The surprise lasted only a moment. Lupin collected himself and gestured them inside.
Once they were seated, he poured them each a glass of warm water and smiled at Sherlock.
"Harry tells me you went to scout the grounds? How did you find Hagrid's setup, anything worth noting?"
"We ran into Moody in the corridor just now," Sherlock said, bypassing the question entirely.
Lupin's smile faded at once. He leaned forward slightly, his expression sharpening.
"Did he ask what you were doing there?"
"He did. I told him we were coming to see you."
"What did he say?"
"He said that as a judge, he couldn't allow a professor to give us private coaching before the task, that it would violate the rules of the Tournament."
"And yet you came anyway."
"Because I told him we weren't here about the Tournament."
"Did he believe you?"
"No."
A silence settled over the room. Lupin looked at Sherlock, entirely at a loss for how to respond.
He considered himself a reasonably sharp man, not in the same league as James or Sirius, perhaps, but no fool. And yet this brief exchange left him with the peculiar sensation of having missed a step as though the two of them were operating on a frequency he couldn't quite tune into.
Gemma, seated beside Sherlock, wore an expression of patient resignation. She couldn't blame Professor Lupin. The asymmetry of information was simply too great. No one in their right mind would expect that the highly regarded Auror Alastor "Mad-Eye" Moody a judge in the Triwizard Tournament, no less was actually a former Ministry official walking around in a stolen identity.
It was the sort of thing that defied belief. Almost anyone would struggle to make the leap.
Fortunately, Sherlock didn't let the silence drag.
Seeing that words alone were creating more confusion than clarity, he reached into his pocket, drew out the Marauder's Map, and laid it flat on the table between them.
Lupin knew this map better than almost anything. He had helped make it, after all. He had heard from Harry that Sherlock had taken it to the Quidditch pitch earlier, and while the purpose had been unclear to him at the time, he had simply told Harry with a smile that Sherlock surely had his own reasons.
But now Sherlock had laid the map on his desk again, and it was pointed squarely at him.
The irony landed faster than he was ready for.
He didn't understand the intent. He simply bent his head and began to study it carefully.
Remembering that Sherlock had mentioned running into Moody in the corridor, Lupin instinctively started his search from his own office and scanned outward.
What he found made the blood drain from his face.
He looked up sharply at Sherlock, his eyes wide with shock.
"Barty Crouch? What is he doing at Hogwarts? The Ministry said he was at home, recovering—"
"The issue isn't Crouch himself, sir," Sherlock said quietly, his gaze resting on the map. "As I said—the person Gemma and I encountered was Moody."
Lupin went very still. His pupils contracted.
Anyone else might not have grasped what Sherlock meant. But this was Remus Lupin one of the Marauder's Map's own creators. And just last year, he had stood witness as Sherlock used this very map to expose Peter Pettigrew, a man who had spent over a decade disguised as a common rat.
So, the moment the words left Sherlock's mouth, he understood precisely what they meant. He bowed his head again, this time looking long and hard at the map, scrutinizing every detail.
Unlike before, this search took time. He did not rush, and neither did Sherlock, who simply lifted his glass and took a quiet sip of water.
If Sherlock wasn't in any hurry, Gemma certainly wasn't either. She waited in silence though her gaze moved steadily back and forth between the two of them, quietly turning things over in her mind.
Whatever this was, the relationship between Sherlock and Professor Lupin was clearly something more than ordinary teacher and student.
When Lupin finally raised his head again, his expression had changed entirely. His voice, when he spoke, was low and rough.
"Polyjuice Potion?"
"That would be my current assessment, yes."
"Why would he do this?"
"Because of Harry's dream."
"Not him—him?"
"It seems rather obvious."
"We need to go to Dumbledore. Right now." Lupin rose to his feet, his movements urgent. He had grasped the gravity of the situation.
"That is precisely why I came," Sherlock said, standing as well, his composure unchanged.
This time, the exchange between them was frictionless instant understanding, no hesitation.
Gemma, meanwhile, was completely lost.
In the space of a few minutes, she was the one without enough information. The pendulum had swung.
She couldn't keep up with either of them, and was left sorting quietly through the fragments she'd managed to catch when Lupin spoke up:
"Miss Farley, will you be coming with us?"
He addressed the question to Gemma, but his eyes moved instinctively to Sherlock.
The implication was clear enough. This affair was dangerous whatever conspiracy lurked beneath the surface might run deeper than anyone yet imagined. Gemma, as a graduate, had no real reason to be drawn any further in. But out of respect for Sherlock, after all, he was the one who had brought her here, Lupin was willing to defer to his judgment.
Gemma was sharp enough to read the room. She turned to Sherlock at once, her expression full of quiet resolve and unspoken hope. She wasn't going to flinch.
Sherlock thought for a moment, recalling what Gemma had said to him outside the Quidditch pitch, and the rare look of open expectation she was wearing now.
"Gemma can be of help to us," he said.
The words sent warmth blooming through her chest. She couldn't stop the corners of her mouth from lifting.
Finally. He'd actually come around. In the past, Sherlock would almost certainly have stayed focused on the matter at hand and never thought to make room for her. But something, quietly and without either of them fully noticing, had begun to shift.
Even Lupin looked mildly surprised to hear it. But he recovered quickly and gave a short nod. "Alright then. Let's not waste any time."
As a Hogwarts professor, Lupin knew the password to the headmaster's office, which spared Sherlock the trouble of talking their way past the gargoyle. The three of them moved quickly through the upper corridors, their steps brisk but measured, until they arrived at the door.
"Remus, you've been visiting me quite frequently of late," said Dumbledore, who opened the door himself. He looked at the three of them with mild surprise, though his expression remained warm.
"And Sherlock, every time you walk through my door, you bring something unexpected with you." A pause, and then a gentler note. "Miss Farley—I don't believe you've set foot in this office since you graduated, have you?"
"Albus." Lupin didn't wait for pleasantries to run their course. "Sherlock has uncovered something of the utmost importance. It concerns Voldemort."
Dumbledore had not expected Lupin to open with something so weighty. The warmth in his expression receded, and his gaze shifted, slowly, deliberately to Gemma.
He had noticed, with the keenness of long practice, the way she had flinched at the name: the small, involuntary contraction, and then the way her hand had tightened around Sherlock's.
He understood that she was here because at least one of the two and by all appearances, it was Sherlock who had chosen to bring her. And there were things he needed to say before any of this went further. He owed that much to everyone in the room.
"Miss Farley." Dumbledore's eyes, behind their half-moon spectacles, became suddenly and quietly piercing the kind of gaze that seemed to pass through glass and cloth and bone and reach directly into a person.
"Since you are already seated here, I will not ask you to leave. But I must ask that everything you hear and see within these walls today, you share with no one. Not your parents. Not your closest friends. What we discuss touches the safety of many lives, and may have consequences for the entire wizarding world."
In that moment, Gemma understood something she hadn't before: that the kindly, silver-haired old man she had passed in corridors for seven years was someone she had never truly known at all. The effortless authority that surrounded him, and the depth and stillness behind his eyes, made the weight of the secret she was about to carry feel suddenly, unmistakably real.
She glanced once more at Sherlock.
She had been right to come.
She straightened and met Dumbledore's gaze.
"I understand, sir. I won't tell anyone."
"Good." He gave a single nod, then turned to Lupin.
"Then, Remus please. Tell me what has happened."
Lupin drew a slow, steadying breath.
"The Moody at this school," he said, each word deliberate, "is an impostor."