"Sherlock?"

The boy was leaning back in his chair, eyes unfocused, fingers playing through the air in odd patterns.

"Sherlock!" By the fifth time, he seemed to have heard.

"Hm? Oh, John." Sherlock sounded vaguely disappointed.

John repositioned his cane and looked around the empty third-floor classroom, waiting for all of Sherlock's attention to focus within the room. "I just had an interesting little chat."

"Not a Graphorn," Sherlock mumbled. "Chat? With whom?"

"Friend of yours."

Sherlock's eyes snapped open. "Friend? What friend?"

"Well, he said an enemy."

"Oh," Sherlock looked relieved. "Which one? Anderson?"

"He didn't give his name. Tall bloke, skinny, sort of gingery hair? Adult, but not a teacher. Must be a visitor or something. Sound familiar?" He asked as Sherlock rolled his eyes.

"Yes."

John waited, but he seemed in no hurry to elaborate. "Who?"

"The most dangerous man you've ever met and not my problem just now. What sort of creature has a taste for house elf?"

"I've been over it a dozen times since the other night, and it makes no sense –"

The door opened and Lindsay and Molly peered in.

"Oh, sorry," Molly said immediately. "We were just looking for a place to review our essay," she held up a roll of parchment.

"Come on in," John invited, ignored Sherlock's little snort of disapproval. "We're practically done anyway."

Sherlock rolled his eyes and looked out the window, but just as quickly had snapped his head back around. "You. You were the one who found the elf, weren't you?"

Molly cut her eyes around the room, suddenly fidgety. "Yes."

"Sherlock," John warned. "This may not be the time."

"I know about it," Lindsay announced. "Molly told me yesterday."

Molly looked abashed. "It just slipped out. Besides, she's the only one I've talked to about it."

John nodded his understanding. Sherlock didn't seem to be paying attention.

"And you?" he demanded, turning to Lindsay.

"It's Lindsay. Remember? I introduced you yesterday in Herbology? She was in our group for the sopophorous beans."

Sherlock stared blankly. John was only marginally surprised, as Sherlock had spent most of the class muttering to himself about Professor Sprout's obvious preoccupation with her diminished mandrake population and its effect on her lesson planning. He started to introduce them again, only to realize that Sherlock once again was talking to himself.

"It doesn't make sense!"

"What doesn't?" Lindsay asked, turning a chair backwards and seating herself on it.

"There are no creatures in our world that have such a strong taste for elf meat that it will sneak into a school full of wizards and crammed with easier targets, eat one elf and vanish –"

His eyes slid out of focus, whole body frozen, one hand mis-dismissive wave.

"Oh…"

"What?" John asked, wincing at himself. The word was already becoming overused.

"It vanished. Don't you see? We looked everywhere it possibly could have gone. We didn't see any signs of concealment or any place where it could have gone out of the castle. The ghosts haven't seen or heard anything, and they assure me that the staff haven't found anything either."

"The ghosts…" John stopped himself before parroting yet another sentence. "Right then, what does that mean?"

Sherlock's grin slipped. "You don't see?" John and Molly shook their heads. He seemed to deflate. "You look like a pair of Bundimuns. Is it nice not being me?"

"It has some way of making itself invisible, "Lindsay interrupted. She continued slowly, stringing her ideas together. "If there have been absolutely no signs, it had to have left no signs, which means invisibility or apparition."

"But you can't apparate within the castle," Molly said, catching the rising comprehension.

"Right, and we're almost certain this was a creature, not a wizard. At least, I hope so," Lindsay continued. "So, if that's true, an invisibility cloak isn't looking likely. What options does that leave?"

Sherlock interrupted, looking a bit piqued. "A magical creature that can turn itself invisible and has an apparently intense craving for house elf flesh."

"Well, that narrows it down," John said.

"Yes, quite a bit," Sherlock said. "It doesn't exist."

The four of them were silent for a moment, then John offered. "I could go talk to Hagrid on my free period. He'd know about a creature that dangerous."

"Hagrid is about as reliable as Trelawney's tea leaves when it comes to information," Sherlock said. "I might have a different solution. Another Ravenclaw – Victor Trevor – is doing an independent study this term about the use of potions to identify wizarding criminals. He's developed some tests very similar to what muggles use for DNA testing. I have a sample from the bite marks on the elf. Victor will jump at the chance to try out his tests, and Professor Slughorn allows him in the potions laboratory unsupervised."

"And not you? I'm stunned," Lindsay said drily.

Sherlock shot her a look. "Considering you are in your seventh year and still haven't perfected a shield charm, that must have been a regular occurrence."

"I imagine you had to learn that one by primary school or you never would have survived long enough to get to Hogwarts."

"Alright, you two," John interrupted. "Enough. And what's this about a shield charm?"

Sherlock rolled his eyes. "She's wearing foundation. She wasn't wearing any yesterday, so I assume make up is not a daily habit with her. That makes it important. It's especially heavy on the right side of her jaw. Most girls apply makeup in strokes going down the face, so for there to be excess under the jaw would have to be intentional. If you look closer, there's some redness under the foundation – a fairly wide swath. Not a fingernail scratch , then. Regardless of how clumsy a person is, it's hardly reasonable to assume they would trip and scrape their chin beyond age 4, but any more serious fall would have left more serious injuries. Obvious conclusion: this wasn't self-inflicted. I can think of six minor jinxes or hexes that would cause a person to fall forward without the ability to catch themselves, and judging by her friendship with you, John, I'm guessing she also made enemies last year. The fact that the injury happened at all tells me her shield charm is not the quickest or strongest."

John had stopped listening several sentences back and was examining the scrape with care over Lindsay's protests.

"Shut it and let me make sure there's nothing more serious the matter," John commanded, siphoning off the makeup with his wand. The skin was red and raw, but appeared to have begun healing already and had none of the telltale signs of a cursed wound.

"You think I didn't already check?" Lindsay asked as he leaned back. "It was Alexander Mulciber who cast it when I met him coming around a corner. I wasn't going to take any chances."

John suppressed a sudden urge to laugh. Mulciber had been the Carrows' pet last year, and by extension, the particular target of DA pranks. Small wonder he'd jinxed Linsday. "I can fix that up for you," he said, waving his wand in a diagonal pattern so the redness receded and the skin closed itself. "There. Did you give him anything in return?"

Lindsay smirked, but said nothing.

"Mulciber was one of the two who jumped me on the train," Sherlock said.

"Not that I think we have time for the full list – but what made them fight you?" John asked.

"Well, the immediate cause was my question if Moran's girlfriend knew her rival was Mulciber, but there were other inciting comments as well. People always get so offended by the truth."

John was relieved he was not the only one staring at the skinny 15-year-old. Lindsay was right; it was something of a miracle the boy had lived this long.

"Well," Sherlock said, rubbing his hands together and bounding to his feet with sudden energy. "I think I'll head back to the dormitory and collect that sample to give to Victor."

He had only gone a few paces when the sound of many hurrying feet in the corridor informed them that the free period was over. They were all headed to the same classroom, but Sherlock hung back, letting the girls go on ahead.

"Your friend should be more careful," he said, his voice more annoyed than concerned. "Slytherin House as a whole is spoiling for a fight – anything to cause trouble in the other houses, but especially Gryffindor."

John shrugged. "Lindsay can take care of herself. There's a reason her shield charm isn't her quickest."

"I was thinking more logistically. I don't doubt McGonagall would slap stricter regulations in place in a moment if she thought it would help keep the students safe. The last thing we need is a duel in the courtyard. I have things I need to do, places I need to examine in regards to this attack, and I can do that much easier without bothering with extra rules to duck around."

"What places?"

Sherlock waited until a trio of Slytherins had shoved past. "I want to have another go at the entrance hall when no one else is around. I have an idea which might give us another option besides invisibility, but I need to be certain no one will interrupt me."

Their chance came that evening. Sherlock showed up at the Gryffindor table during pudding, plopping himself alongside John and ignoring Lindsay as he spoke rapid-fire.

"There's a mandatory meeting in each common room tonight at 8. Meet me in the entrance hall at 8:05 and we can have a look round."

John laid down his spoon. "A mandatory meeting," he said slowly, cutting his eyes to Lindsay. "Right, then, I'll just ask Professor Smith very nicely if I can skive off, shall I?"

Sherlock rolled his eyes. "Just sneak out."

"The portrait hole doesn't lend itself to sneaking," Lindsay said. "The Fat Lady would rat on you in 2 seconds."

Sherlock looked startled, as if he hadn't noticed Lindsay before now. "So think of some excuse to tell her."

"What we really need is a diversion," Lindsay countered. "If we could distract everyone long enough to get the portrait hole open and closed, the Fat Lady might be convinced to keep quiet when we get back. She loves a chance to spy on ruckus in the common room."

"We?" Sherlock asked icily.

"Yes," John said before Lindsay could reply. "Her plan, she gets to be a part. Besides, another set of eyes can't hurt."

Sherlock very nearly pouted. "What's the diversion, then?"

Lindsay smiled. "Peeves."

The preparation was relatively simple. Peeves was more than eager to abandon his post at the library entrance, where he had been tossing ink pellets at anyone coming or going, and follow them to the Gryffindor common room, where he sneaked in under John's robe hem. The idea of pranking the new professor seemed to excite him more than anything since the Weasley twins made their flashy exit from the school three years earlier. The only difficulty came in keeping him in check until the proper moment. The poltergeist finally agreed that his access to the common room was reward enough. He'd been scrupulously kept out of the dormitories for all four houses since the founding of the school, a fact that was making John uneasy.

"How do we get him out?" he hissed as he took his place in a chair near the portrait hole.

Lindsay gave a miniscule shrug. "Either they'll have taken care of it by the time we get back or…" she paused and a shade of disquiet fell across her face. "We'll figure it out. Maybe get him into Slytherin in exchange for getting out of Gryffindor."

Professor Smith walked in, greeting their worried faces with a wide smile. "Why all the gloom and doom? It's a meeting, not an execution. Here!" He twirled his wand impressively in the air. Nothing happened. With a resigned sigh, he reached into the teacher's robe he still wore and pulled out a large bag from Honeydukes. "Here, Peakes, start this around, won't you?"

He waited until the first cluster of students had collected their toffees before proceeding with roll call. John, eyes on the curtain where Peeves lay in wait, listened impatiently for the W's. They would be late to meet Sherlock and somehow he didn't like to think of the boy wandering around the hall doing Merlin knew what by himself.

"John Watson."

"Present," he said with more enthusiasm than necessary. Lindsay dug his elbow surreptitiously into his ribs, but he knew better than to react while Smith was still watching.

"Constance Willinsnope."

"Present."

Constance was behind Smith. Lindsay and John positioned themselves closer to the portrait hole as he turned his back to them.

"Oi," John hissed in Lindsay's ear. "That hurt."

"Then stop acting like you've never sneaked out before, Frankie First-Year," Lindsay said, giving the curtain a firm nod.

Peeves took the signal. The air in the common room was suddenly bespeckled with small black balls, then they dropped, splattering the students below with ink. Over the Gryffindors' outraged cried and Professor Smith's inarticulate shouts rose Peeves' cackle as he zoomed about, dropping his second shower of pellets. John and Lindsay acknowledged his flourishing salute and ducked out the portrait hole.