John nearly threw the post owl out the owlery window in his haste to get to the Ravenclaw common room. Never mind the fact he didn't know the password, John was prepared to hammer on the door until Flitwick himself came to ask what was the matter. He'd just rounded the corner onto the correct corridor when he saw a boy ahead in a blue-trimmed robe. The Ravenclaw turned at the sound of his footsteps, and John recognized Victor Trevor, the boy who had done the potions work for Sherlock.

"Oh, you're –ah, Holmes' homework partner, aren't you?" Victor said, smiling at him. "You're up early."

"You, too," John said, returning the smile instinctively, though his mind was hardly processing his words.

"I rather foolishly set three potions to mature in the laboratory Friday evening late – they needed two counterclockwise stirs and some ginger root at 6 a.m. and now I'm heading back to bed."

He was fairly certain he shared the laugh with the boy, but he was more focused on catching up to him than anything else. "Listen, I need to see Sherlock – any chance I could come in with you?"

Victor hesitated. "It's a bit early, don't you think? I've seen Sherlock when he first gets up, he's no morning glory. I think the last time someone woke him before he was ready, the kid ended up turning in his final potions essay in Gobbledegook."

"I'll risk it."

Victor looked him up and down. "Something wrong?"

"No, just –" John cast about. "Homework."

They reached the arched doorway, but rather than speaking a password, Victor simply knocked on the eagle doorknocker. The bird's beak opened, and a woman's voice spoke.

"Does the wizard learn from his wand, or the wand from the wizard?"

Victor frowned. "I hate wandlore. Stuff and nonsense if you ask me. But I don't think that's the answer she's looking for."

"You mean there's not just a password?" John asked, looking back down the hallway toward the stairs. He would have to hurry or Madam Pomfrey would waste time and energy worrying about him rather than the patients who needed it.

"No. Daily riddles, courtesy of Rowena Ravenclaw," Victor said, passing a hand down his face wearily. "Should have just let the potions spoil."

He though a moment longer. "They – they both grow together… like stem and root."

"Insightful," said the voice, and the door swung open.

Victor gave a sigh of relief and dashed through. "I can still get another couple of hours of sleep before breakfast ends. Nice seeing you, er –"

"John."

"Right. John. Well, have a good day, John. I'm off."

"Wait!" John said, moving forward despite staring around at the pristine room that bore little resemblance to the Gryffindor common room. There were far too many breakable things for his comfort. "Which room is Sherlock in?"

Victor pointed to a sofa that had been dragged out of alignment with the others and was positioned facing a window. "He usually drops off there."

Sure enough, Sherlock was sprawled across the blue velvet cushions, a book dropped against his left cheek and a roll of parchment tucked under his right arm.

"Sherlock?"

The boy sat up so fast the parchment ripped and the book toppled to the floor. "What? What's – I'm – oh, John!" He pulled a slim volume from underneath him, wincing. "Terrible sleeping plan. Books on the floor from now on. What happened?"

"Sorry?" John said, his brain still separating the string of words.

"You're in the Ravenclaw common room – traditionally not a place one would find a Gryffindor at this hour of the morning. It's not NEWT arithmancy, John. What happened?" Sherlock got up, whipping his tie from his neck and tucking it into a robe pocket.

"Poisonings. Three of them so far. They've got round puncture marks on them – not all in the same spots – and they feel like they're burning up from the inside."

"House?"

"Two Gryffindors and a Hufflepuff."

"Year?"

"Seventh years so far."

"Gender?"

"Two boys and a girl."

Sherlock frowned.

"Do you think it's the monster-thing? Didn't Winky say it had a stinger?"

"Could be," Sherlock said, turning on his heel and heading for the door. "No way to know until we can compare –"

He turned just as fast, striding toward the stairs to the dormitory. "I need to get Victor."

John filled both Ravenclaws in on the situation on their way back to the hospital wing, over Victor's sleepy grumblings. He wasn't sure about letting Victor in on the situation, but it given that he was the only person who both knew about the samples from the monster and had the potions expertise required to compare the two, it seemed inevitable. Lindsay was waiting outside the hospital wing, and the foursome entered together.

A fourth bed was occupied, a boy writhing under the sheets. A green-trimmed robe was flung across the chair by his side. Madam Pomfrey was hurrying over with a jar of bitterroot paste.

"What did you learn?" she asked, taking in the three other students with barely a blink.

"Nothing yet," John said, pushing Victor forward. "But he's got a... a sample from a creature…"

"A creature I found at the edge of the forest," Victor said smoothly. "It was dead, decomposing, and I'd never seen a body like it. I took some DNA samples and I've been trying to use my potions to discover what it is. John thought there might be a connection between my experiments and the poisionings."

"Do you still have a sample?"

Victor nodded and walked toward the cauldrons still set up in the corner. "May I?"

Madam Pomfrey nodded. "Professor Slughorn went back to his study to look for another poisons book after Noble was brought up. You can work with him when he gets back. John, it's time to reapply the salve." She glanced at the other two. "What can you do to make yourselves useful? If the answer is 'I don't know,' leave now. We don't need more people taking up space."

"Sherlock can work with me," Victor said, motioning the boy over. "He knows my methods."

"I can do anything you need," Lindsay said quickly. "I'm good with potions, or I can help with the salves, or –"

The Slytherin boy moaned loadly.

"John?" Madam Pomfrey asked distractedly, leaning over the boy.

"Lindsay can help me."

He took the jar of salve from Madam Pomfrey and nodded Lindsay to the Slytherin's other side, grasping the boy's upper arm to hold him steady.

"It's Mitch!"

It took Lindsay's exclamation for John to recognize the blonde boy, who had spent half the year working with the DA. His inside information on the workings of Slytherin House had been invaluable, until Amycus found out who was behind the leak and had beaten the boy to the point that Madam Pomfrey had stepped in to stop him. After the boy recovered, Neville had actually ordered him to stay away. He still sported scars just below his left eye and across the bridge of his nose. It had been over seven months since John had seen the boy face to face, and the interim had wrought what seemed to be a decade of maturity in his features.

"Hold him steady, the mark is here on his shoulder," Madam Pomfrey snapped, holding a dropper with the cleansing flush they'd been using on the wounds.

They held him down as Madam Pomfrey dropped the solution into the wound and covered it with a bandage. Mitch let out a choking scream and lashed out. John leaned away to avoid the flailing fist.

"It's alright. It will help, I swear. You're going to be fine." There was no sign that the words had registered at all, but it made him feel better to say them.

Madam Pomfrey's face was drawn as she stood back. "You sent the owl?"

"Yes."

"The others are resting more comfortably. It might be something that will pass, or it might just be getting worse." She tucked an errant grey strand of hair behind her ear and straightened her shoulders. "Give him the sleeping draught and then apply the bitterroot salve to all four. I'm going to try and find bag of powdered valerian so I can make more if we need."

The Draught of Living Death was already on the table beside Mitch's bed. It was the only one that had been strong enough to work on the others. John poured a measure and dribbled it into Mitch's mouth gently. The effect was almost instantaneous. The tight muscles relaxed and the boy's eyes slid shut.

"Well, that's one step sorted," John muttered, feeling his own shoulder relax slightly.

Lindsay stepped over to Parvati. "Do you remember when we had that scrofungulus breakout in the DA last year?"

John unwrapped the bandage around Robert's forearm and gave a hoarse chuckle. "Merlin, yes. I don't think I got a full night's sleep for a fortnight."

"You looked like you'd been trampled by thestrals. That may have been the first time I realized you weren't just a ladykiller."

"Oh?"

Lindsay grinned at him before returning her attention to unwrapping Parvati's bandage. "Let's just say that all I knew of you prior to that was what I heard before stuffing a pillow over my head in the dormitory at night."

"It's not my fault if girls want to talk about me. I've never done a thing to encourage it." John took a large dollop of the orange salve and passed the jar to Lindsay. "Put a thick enough layer that it stands up off the puncture at least a quarter inch. Don't be afraid to press it in a bit, either. Be sure you cover it with the bandage, or it'll just soak into the sheet instead."

Lindsay nodded. They worked in silence for a few moments.

"As I recall, you were one of the last to come down with it," John commented. "One of the worst cases, too. I thought your face might explode."

"If one must be sick, it is better to be spectacularly sick," Lindsay retorted.

"Less talk, more work," Madam Pomfrey interrupted, bustling past with a small burlap sack. "You can see if those two need any help with the potions. If not, I've got some linens here that need washing."

"She doesn't let the house elves touch the hospital wing linens if it's something that can be transmitted to them," John explained in an undertone. "They're immune to most common Wizarding diseases, but she once lost four elves to an outbreak of dragon pox."

They had both been in the Wizarding community long enough to realize how rare this type of concern was. There were few things that had boosted John's opinion of the school nurse quite like that knowledge. He acknowledged Lindsay's surprise with a nod and turned to the two Ravenclaws.

"Anything we can do?"

"Yes, stay away." Victor said, his tone so preoccupied it was hardly even harsh.

"This new case – the Slytherin," Sherlock said, peering into his cauldron. "Is he also a seventh year?"

"No. Sixth."

"So we can rule age out as a factor. And the only house not affected thus far is Ravenclaw. Interesting."

"Yes," Victor said, casting a glance over at Madam Pomfrey, who was setting up a mortar and pestle at the other end of the ward. "Most interesting."

Sherlock looked up at him. "Significant?"

"I think that's more for you to say."

All three of them looked their puzzlement. Victor rolled his eyes.

"I may not be quite so quick as you, Holmes, but I'm in Ravenclaw for a reason. This stuff gives every indication of matching that sample you gave me – though I won't know for sure till I let these potions brew. It's apparent that the two things are linked, and now I find that the only house to remain unscathed is your house."

"Yours, too," Sherlock said, his voice calm and quiet. "What are you suggesting?"

"I'm just wondering if you don't have something you need to tell. Some experiment of yours that seems to have gotten out of your control," Victor said, his voice nearly paternal. "I wouldn't dream of saying it was intentional."

"Don't be a lobalug, Trevor," Sherlock said impatiently. "I have nothing to do with this."

"Then I don't see any other explanation."

The Ravenclaws glared at each other for several moments.

"There's work to be done," Madam Pomfrey called. "Have you found anything out?"

Victor turned to face her. "Only what we had assumed – it's a delayed reaction. They were probably stung mid-day, or late evening in the Slytherin's case. Whatever this is, its purpose is to make the victim suffer – for a long while. It doesn't react like any creature venom I've encountered before, but it does seem to be connected to the samples I took."

"Can we go find the body?" she asked.

"I went back the next day to get more tissues, and it was gone. I assumed the thestrals ate it or Hagrid had buried it," Victor said.

John couldn't help but admire his smooth lying skills, even as he distrusted them. Then again, most of the Ravenclaws he knew had that ability to bluff their way out of anything. It had held Michael Corner in good stead during his many escapades for the DA the year before.

"Well, then, the rest of you make yourselves useful. We won't solve this waiting for a potion to boil."

Several hours later, Charles Boot from Ravenclaw and Dennis Creevey from Gryffindor were also brought in. It was late afternoon when the owl returned from St. Mungo's, saying they would send a healer the next day. An outbreak of spattergroit was stretching their resources thin. They suggested Madam Pomfrey keep the children comfortable, and come by apparition to fetch someone if anyone took a turn for the worse. Madam Pomfrey had nodded grimly and forced them to leave the hospital wing to get some rest and food, promising to call John back if a need arose.

Victor bade them farewell and returned to Ravenclaw tower before dinner. The other three trooped into the Great Hall and sat at the far end of the Gryffindor table. None of them had much appetite, John and Lindsay due to concern, Sherlock due to preoccupation.

"How on earth did the creature get at them all? And at such different times? Charles and Dennis would have been in their dormitories, or common rooms at least," he mused. "It doesn't make any sense. You can't apparate in the school. How is it getting in and out of the castle so easily? And in so many places?"

"I don't know," John said wearily, staring at the roll in his hand rather than eating it. "And going over it again isn't likely to help."

"We need to get into that study," Sherlock said.

Lindsay and John blinked at each other, then at him.

"You said you can't open the lock," Lindsay reminded him "Shouldn't we be looking for wherever the creature is hiding? I think we should look in the forest before it gets dark."

"The key lies here in the castle, though. I'm sure of it. Those poisonings this morning convinced me."

"So you think the creature is somehow connected to the Transfiguration study. It still doesn't fix the problem that we can't get in."

Sherlock smiled. "But if the creature can use an alternative means, so can we."

They waited until twilight, when most of the students were returning to their dormitories or the library to do the homework they'd put off till then. The courtyard was completely deserted when they crept along the wall till they stood beneath the Transfiguration study window.

"And you're sure the window isn't magically sealed?" John asked as Sherlock drew his wand.

The boy didn't bother to reply, just twirled the wand like a lasso till it released a shining magic rope that soared upwards and seemed to plaster itself onto the window ledge. "No better time to find out."

"You've used this spell before? You're sure that rope will bear weight?"

Sherlock rolled his eyes. "When I want to be smothered, I go home. Stop playing Mummy and help me test it."

Sherlock leaned back on the rope, but it didn't budge. With a smirk at John, he put a foot up on the wall.

"I'll go tell you what I see."

"Not bloody likely," Lindsay exclaimed a split second ahead of John.

"We'll all be up there," John said firmly, "Or none of us."

Sherlock rolled his eyes and started to climb. John cast impervioscurrsus on an area wide enough to cover any direction he might fall, but the boy was a natural climber, scaling up the wall in record time. He seated himself on the window ledge and gave a smirking wave down to them before peering inside.

Even from below they could see his start of surprise. He tried the window, but from the rattling, it seemed to be locked. A few seconds and a spurt of wand light later, it was open. Sherlock swung his legs through and called down to them in a hoarse whisper.

"Get up here as quick as you can."

"Dangerous?" John asked, letting Lindsay grab the rope, but keeping her from starting her ascent.

"Not sure," Sherlock said finally. "It's some sort of blue box."