"Can you open it?" John asked after Sherlock's silent examination of the lock had stretched to uncomfortable limits.
"The oil deposits are heaviest on this circle and this one," Sherlock said, indicating an outer ring and one just inside it. "Equally heavy, in fact, as if both hands are used to move them simultaneously. Unfortunately, after that, the sequence becomes impossible to detect, and with this circular design, it would take me until tomorrow morning at the earliest to crack it, and I don't think we have that kind of time."
John scratched his head, irritation warring with concern. Out in the stairwell, a peal of laughter and the pounding of shoes announced a group of students heading up, likely to their dormitories. The noises bounced faintly off the stone walls of the corridor, seeming much louder than they were given Sherlock's all consuming concentration.
"You said you had a way to find out about Smith right away," Lindsay said finally. "Don't you think it's time we used that?"
Sherlock's face contorted into an expression rarely seen on faces older than six. "We're not quite so desperate just yet."
"What are we waiting for, then?"
Sherlock turned around and leaned back against the wall, steepling his fingers under his chin. "The creature entered the kitchens through the flue, and exited the same way. No one has seen it do this before, and we've seen its trail to the balistrarias with our own eyes, so it's breaking its routine. Why?"
"It found a quicker way in?" John suggested. "Why bother with all the hallways and people if you can get straight at the elves?"
"Yes, but it's only just now chosen to come in this way. After killing eight others? There's a reason. The flue from the kitchens leads out on the north side of the castle – the side facing the Black Lake. In fact," he stood up straight suddenly. "It should be just round the corner from this room. The windows for this study face the courtyard, don't they? It would be just a short climb from the Astronomy tower."
Before Lindsay or John could comment, Sherlock shook himself. "Listen to me. I'm trying to find facts to fit my theory. Childish. Ought to know better by now. Let's begin again. It's obvious Smith is hiding something in this room, and despite being a fairly spectacularly inept wizard, he's locked it in a way that it presumably only he knows how to open. It's also clear that whatever or whoever the creature is, it's changed its habits of late – it took the elves with it rather than eating them there. Part of it, naturally, is that the return of the students will have made it much harder for it to feed. But the fact that it came in daylight today also seems suggestive."
"Something to do with the Saturday schedule?" Lindsay said.
"Perhaps," Sherlock said, heading back toward the stairs. "Regardless, there's an easier way to check our theory about this room being used."
"Outside?" John asked.
Sherlock turned, actually smiling, "Yes. Shouldn't be too difficult to identify the direction the scratches take once they leave the balistraria."
"You do realize it's about to pour puffskeins out there, don't you?" John protested.
"Afraid of thunderstorms?" Sherlock asked with light mockery, continuing down the stairs.
"No, but I don't fancy scaling a vertical wall in them. You'd be asking for a fall."
"Good thing you've got that custard-spell, then isn't it?"
John set his jaw in irritation. Lindsay shrugged at him.
"It hasn't started raining. Maybe we'll be done before the worst hits."
By the time they reached the doors, they were caught in a stream of wet students coming in from the yard. Lindsay and John only took a couple of steps past the archway when the sting of the wind-driven rain convinced them back into shelter. The flagstone courtyard already had currents flowing toward the openings onto the grassy areas. Even Sherlock only ventured a few steps further before returning to the doorway, hair plastered down on his face. The setback would have been more irritating for all if Sherlock's irritation hadn't been so amusing.
"So we just have to wait for it to end?" he huffed, waving his wand across his robes to dry them.
"Or cast an anti-rain spell strong enough to drive all of this away," Lindsay observed.
Sherlock growled. "I know the theory of meteorological spells, but I've never tried one, and certainly never one of this magnitude."
"That surprises me," John said, chuckling at the glare from under the fringe of hair that Sherlock was in the process of drying. "No, really. I assumed you would be the type to be casting hurricanes in your backyard when you were supposed to be taking an afternoon nap."
"When I could get my hands on a wand at that age, I was more interested in experimenting with transfiguration."
"Of course you were," John sighed. "Well then, no wall climbing for tonight. Any other big ideas? Dinner should be any minute."
"We have homework that ought to be done," Lindsay said reluctantly. "I'm betting that essay for Flitwick isn't going to be something we want to be starting tomorrow night at curfew."
"I was planning on doing that during History of Magic Monday," Sherlock said.
"Yes, but some of us don't write at the speed of light," John countered. "Besides, no one said you had to do homework tonight, just us mortals." He frowned. "Though we still haven't finished the lethifold diagram or the essay."
"You haven't?" Lindsay asked, surprised. "Molly and I had that practically completed by Thursday."
"You have a Hufflepuff partner," John said pointedly. "I don't."
He hadn't meant it as a goad, mainly because he was quite certain such things didn't work on Sherlock Holmes, but the 15-year-old had furrowed his brow at the words. He seemed to be sorting through some unfamiliar information in his head.
"When will you be working on it?" he asked, his words strangely halting.
John shrugged. "Dunno. Probably head to the library after dinner."
Sherlock set his shoulders as though about to face down a harpy. "I'll be there."
All told, it wasn't the least productive night of homework John could remember, but it was certainly stiff competition for the night the Daily Prophet reported Harry Potter had been sighted leading Muggleborns out of the ministry. Sherlock found the lethifold tediously boring, and spent most of the time muttering about alien information and how Professor Sinistra had been absurdly close-minded about the subject when he'd asked her in the Great Hall. John had managed to get a fair chunk of the Charms essay completed, and the lethifold assignment lacked only another foot of parchment. It was with a pleasant glow of purpose that John had headed into the dormitory that night.
He was jolted from a dreamless sleep by a moaning wail. He had one foot on the floor and was kicking the other out of the sheets before he realized that the sound hadn't come from within his room. The interrupted snores around him confirmed he was not the only one to hear it. He nearly tripped over Harold Fortescue, the prefect, in the hallway. Their muttered, confused apologies were interrupted as the sound came again, more like an agonized groan.
"Above," Harold said, heading up the steps.
They met two students coming out of a room, supporting Dean Thomas between them. The boy was bent nearly double, clutching at his side.
"He just started yelling," one said, his face white in Harold's rather shaky wandlight. "He's all clammy, too."
John stepped up to Dean, detaching his grasping fingers from the pajama fabric. There was no bloodstain apparent on the clothes.
"It burns!" Dean gasped out, keeping another moan in his throat with an effort. "Worse than fiendfyre."
"Someone go get Madam Pomfrey and Professor McGonagall," John ordered, easing Dean into a semi-reclining position on the steps. "Go on!"
He jerked Harold's wand closer and moved the shirt up, revealing a small puncture wound just below Dean's right ribs. It was small enough to have been made by a quill, and likely hadn't bled more than a drop, but the heat emanating from the flesh around it was enough to confirm that it was no ordinary injury.
Dean curled into himself again, knocking aside John's probing hands. "Making it worse," he ground out.
"Sorry, mate, but I'm going to have to," John said firmly.
The sound coming from Dean's mouth was half-feral, but John patiently pried his hands away from the injury.
"Trust me, Dean. You're going to be okay. You have my word."
There was little more to be gained from examining the puncture. John took only long enough to realize the wound was almost perfectly round without any tearing at the edges before letting Dean curl up again to wait for Madam Pomfrey. The boy was in enough pain to not mind whimpering like a child in front of his classmates, a rather ominous realization. John settled back on his haunches and looked up at Harold. The boy had been asked to remain outside the doings of the DA the year before, as his position put him at a greater risk of discovery and the younger children still needed a solid leader they could count on. His lack of experience with emergencies showed in every sweat-soaked line of his face.
"Will he be alright?" Harold asked, his voice rasping.
John nodded, not bothering to say anything as Dean shuddered through another groan beside him. He was surprised they didn't have more of an audience, but there were only three doors open, and the boys seemed content to watch from within their rooms rather than come out and help. John was spared having to suppress his annoyance by another scream – this one higher pitched and coming through the wall. He bolted to his feet.
"Stay with Dean," he commanded Harold. "I'll go see."
He'd only made it up three steps of the staircase to the girls' dormitory when his feet flew out from under him and he slid back down the now smooth pathway to the common room floor. He rolled to the side just in time to avoid Lindsay and Hermione as they tumbled to the bottom.
"It's Parvati," Lindsay said as she scrambled to her feet. "I'm going for Madam Pomfrey."
"No need. She's already been called," John said, holding out a hand to Hermione, who ignored it and bounced to her feet, too.
"She's got a small –"
"Puncture-type wound with smooth edges? Says it feels like she's burning up?" John interrupted.
Both girls nodded.
"Who?" Lindsay asked, not bothering to formulate the full sentence.
"Dean Thomas."
The door burst open and Madam Pomfrey swept in, followed by Professor McGonagall.
"Where's Dean?"
John gestured up the stairs to the boys' dormitory. "But Parvati Patil has the same symptoms."
Madam Pomfrey's kindly face settled into an expression John recognized from the battlefield. "Right. Minerva, go with the girls and see to Parvati. I'll be there in just a moment. John, with me."
The light was grey-blue and fuzzy in the windows before they had a chance to stop and regroup. Parvati, Dean, and Robert Cadwallader from Hufflepuff lay in the three beds closest to Madam Pomfrey's study. They were sleeping, but even their sleep was punctuated by little whimpers and catches of breath that said even Madam Pomfrey's strongest pain potions hadn't been quite enough to relieve their symptoms. They'd swabbed the wounds, taken blood for sampling, and spent the rest of the night doing their best to decipher the source.
John had been able to separate a few drops of a foreign liquid from Cadwallader's blood, eliminating the possibility of it being a curse, but the substance proved impossible to identify. He and Madam Pomfrey agreed it wasn't a simple poison, but beyond that they were stymied. Madam Pomfrey poured over her copy of A Healer's Reference to Poisons and Antidotes but so far had uncovered nothing that matched these symptoms exactly. John spent half the night sweating over a cauldron in an attempt to separate the components of the stuff, only to find them stubbornly fused. He'd duplicated the sample over and over, setting up more cauldrons for Madam Pomfrey to test, but none of them had been conclusive.
"I'm sending an owl to St. Mungo's," Madam Pomfrey declared finally, collapsing into the chair behind her desk and drawing a roll of parchment from the drawer. "They'll have to send someone down."
John, who had cast Scarpin's Revealer spell for the fifth time, merely nodded grimly. "Did that Burning Bitterroot rub do any good?"
Madam Pomfrey shrugged. "I think they're resting more comfortably. But what does that tell us? Bitterroot has been a balm for inflammation since the dawn of time. There's no guarantee that it's counteracting the poison."
Her quill scratched across the surface of the parchment. John's fingers curled around the page of failed theories they'd been adding to for the last four hours, and only with a mighty effort restrained himself from ripping it to shreds. They would need the information to share with the healers when they came. He contented himself with scourgifying an empty cauldron with a savagery that nearly gouged the side of the vessel.
Hermione and Lindsay had stayed with Professor McGonagall to talk to people who knew Parvati and Dean, hoping to find out a common thread they could use. They'd sent a house elf with a message for Professor Slughorn an hour ago, but he had yet to respond. John was doubtful that the old man would be much more help than Madam Pomfrey, but she was unwilling to give up until she'd exhausted all her resources.
John was still working on the last cauldron when Professor Slughorn entered.
"Sorry to keep you waiting, Poppy," he said gruffly. "I was delayed by one of my NEWT potions students who'd heard the commotion in the corridors and wanted to know if he could help. Now, what have we here?"
John tried to write off the immediate burst of irritation as tiredness, but wasn't very successful. Chances were much better that Slughorn had dozed back off after receiving the message, and that put the portly professor on the same level as whoever or whatever had done this. The fact that Madam Pomfrey accepted his explanation without so much as a questioning look made it even worse. He put his wand away and sat in the chair beside Dean's bed, still for the first time since he'd heard the first scream.
"I can't identify this, Horace," she said, motioning him over to the cauldron that still held the liquid. "It's not just a simple poison, but specialis revelio does nothing except swirl it around in circles. And those marks on them – I've never seen the like."
John pictured the marks again – roughly the size of a wand tip, but whatever had made them was razor-sharp. McGonagall had sent a message that nothing that could have caused the wound was found in either dormitory, but that left the whole of the school and grounds as possibilities. None of the victims seemed to have known they'd been hurt, so it was likely something they would brush off – like an ant bite or…
The pieces fell into place. They had been nagging at him throughout the night, but pushed aside in favor of the immediate need for potions or information or bandages.
"Could it be a venom?" he asked, interrupting Slughorn's examination of the cauldron.
Slughorn looked at Madam Pomfrey, who shook her head. "I thought the same, but there aren't any poisonous creatures with only one fang, or a stinger that large. I even tested it for Garuda venom, but it was inconclusive."
"But if there was such a creature, one that could make that kind of puncture mark?" John persisted, getting up from his chair.
Slughorn gave a kindly smile. "Yes, but if we were to base identification on the chance that such a creature might exist, we'd be no closer to a diagnosis, now would we?"
John ignored the condescending tone. "I need to go check something."
"Not likely, young man," Madam Pomfrey said, eyeing him shrewdly. "You're exhausted. You're not supposed to be exerting yourself, and here I've kept you up all night with me. You're going to have a lie-down."
"I'm not exhausted," John protested, voice rising. "I'm 17, for Merlin's sake, not 107."
"What is your idea?" Madam Pomfrey asked, voice softening ever so slightly.
"I – I can't explain it properly," John said helplessly. "But I think I can. I just need to go find someone." He snatched up the roll of parchment from Madam Pomfrey's desk.
"I can go post this for you, and check on my way back. It won't take long, I swear."
Madam Pomfrey met his eyes, and he read the concern there with no small amount of frustration. She still saw the stack of potions bottles and the cane, even though he'd stopped using the lot. In her eyes, he was nearly still a patient. He set his jaw and waited.
"Get on with you, then," she said finally. "But come back as quickly as you can with whatever information you get. I'll want to keep you around till this is settled."