Sherlock was crouching in the far north corner of the hall when they arrived.
"Stay for the whole meeting?" he asked without looking up.
"Just took us a bit to get out the door," John clarified with a hint of irritation. "You can't have been waiting long. Now, what would you like us to do?'
"At the moment – shut up."
It took a tight grip on Lindsay's wand arm to stifle her reaction to the directive. She was strong, but John held on, silently daring her to try anything. She'd just begun another attempt to wrench her wand free when Sherlock rose and dusted his hands.
"No hidden doorways in this entire chamber," he announced. "I've sounded each wall 15 feet up. Nothing. Not even a mouse hole. So, that leaves the question – how did it get out? One can't expect it to skulk in the shadows of a place this crowded all the time."
"So it waited till we left and climbed down," John began. "Then… what? Went out the front door? Up the stairs?"
"What if it went up, but not by way of the stairs?" Lindsay asked.
Sherlock looked slightly miffed. "Just what I thought. The scratches on the stone lead to the rafters. It's hard to see from this distance, but I believe I can make out some scratches on the beam fourth from the right. If that's the case, it could have gone along the rafters down any of these corridors."
"What good would that do it? It would still be trapped inside," Lindsay countered.
"Not necessarily," Sherlock said with no small amount of smugness.
He cocked an eyebrow at Lindsay, daring her to answer. John crossed his arms and watched the two of them, wondering if either had the slightest idea how amusing they looked. Sherlock raised his chin in victory and opened his mouth.
"The balistrarias," Lindsay blurted. "The balistrarias on the astronomy tower."
"Sorry, the what?" John asked before Sherlock could reply.
"Narrow windows in the stonework, open air, originally intended for archers as battle stations," Sherlock answered rapid-fire. "If the creature can fit through them, it would be the easiest way to get in and out of the castle and avoid contact with most of us."
"Well, let's check," Lindsay said, taking off down the corridor before Sherlock had fairly finished speaking.
Sherlock responded by dashing ahead. The two of them kept pace, John tapping along behind, all the way to the spiral stone staircase that led up to the astronomy tower. Lindsay slowed at the stairs, glancing back at John. Sherlock was several stairs up before he realized he was alone.
John jogged the last few yards, feeling their eyes on him.
"You could be a lookout," Lindsay suggested. "You probably shouldn't stress your leg –"
"Damn my leg!" John snapped. Both of them stared. "Sorry. It's just… I'm fine. I'm perfectly capable of walking up stairs. Sorry for holding you up." The apology was sour in his mouth.
"It's okay, we don't even know if this is the right way," Lindsay assured him.
"Wrong."
Sherlock was shining his wand light up at the rafters. He looked down at them, grinning. "Scratches. It came this way."
He came down two steps. "The first balistraria is two flights up. We shouldn't need a lookout down here. We'll hear them coming long before there's any visual confirmation. Both of you keep your eyes open, and if you see anything, just say so and don't touch it." He whirled around and started back up the steps, taking them two at a time. "Nothing worse than people spoiling evidence."
"Oh, he grows on you," Lindsay said in an undertone to John as they came up at their own, slower pace. "I can see why you wanted to come tonight."
"Do you think it's a good idea to leave alone to his own devices?"
"I managed quite well before I met you, John Watson," Sherlock's voice floated to the from around the curve in the stairs. "I'll thank you to leave the protective big brother bit for your actual younger siblings. I've already got one to plague me. And Miss Lovejoy, there was no compulsion for either of you to come."
They caught up and found him actually halfway up the wall, having slipped his shoes off and used his toes to find niches in the stone.
"If you did stuff like this alone, you must have been a frequent visitor in St. Mungo's," John said, setting his cane against the wall and drawing his wand.
Sherlock looked down in confusion. "What are you doing?"
"Keeping you from dying." John waved his wand in a broad circle under the spot where Sherlock clung lizard-like to the wall. "Impervioscurrsus."
"I don't know that spell," Sherlock said in real interest, staring down at the transparent barrier that now stretched beneath him.
"That's because Terry Boot invented it for Dumbledore's Army last year," John said, a trifle impatiently. "It's a bit like landing in a custard – you just sink through and land gently on floor, no matter how fast you were going before."
"Why not just use feather light?" Sherlock asked, edging himself a few inches higher on the wall. The window was almost within reach.
"Because we needed a spell that covered multiple people with ease."
Lindsay's voice broke in. "Have you noticed the scratches on the rafters continue?"
John and Sherlock turned to look at her. She was disappearing around the turn of the stairs.
"There are claw marks on the stone here," Sherlock countered. He turned back to the wall and examined the patterns. "They lead right to the window. You're saying it didn't go out here?"
"Hang on, I'm checking."
Sherlock leaned out from the wall to get a different perspective on the marks. The silence had only settled about 10 seconds when Sherlock let out an impatient sigh. John looked up in time to see his fingers slip off a too-small crevice, and Sherlock drop from the face of the wall. The clear layer of magical protection caught him and he slid through it with a slight squelching sound to the stone steps below. John cocked his head to the right and waited as Sherlock dusted himself off and settled his robes.
"You're welcome," he said pointedly, following the stairs around the curve to where Lindsay was examining the wall.
"The marks are different by this window," she said, eyes still on the wall.
Sherlock dove closer, nose nearly touching the stones. "It backtracked, but only just here. Like it was confused or scared." He grabbed the first jutting stone he could grasp and hoisted himself up again. "Wait." He pointed his lit wand at the wall, smiling suddenly. "These claw marks are smaller. At least 1/16th of an inch."
"Naturally. Why didn't we see that?" John asked with good-natured sarcasm.
"So there are two of them?" Lindsay asked.
"And one is smaller than the other. Male and female or parent and child? Closeness of size suggests either an adult female or a nearly grown child. Statistically, more likely to be child, as one mate would do the hunting while the other watched the young. So this one is ready to be taken on hunting trips – but it didn't go down to the corridor with its mummy or daddy. Why?"
Sherlock was speaking so fast that it took a few seconds for the others to catch up with his words.
"It got scared?" John asked.
"Or something kept it from going along. If I knew what creature I was dealing with, I'd be better able to judge," Sherlock said, inching closer to the balistraria. "Regardless, two creatures definitely came through this balistraria. Vial." His outstretched hand was an order.
John conjured one and levitated it up to Sherlock. The Ravenclaw transferred his wand to his teeth and used one of the fingers from the hand clutching the wall to scrape something from the crevice beside the window.
"What is it?" John asked.
Sherlock answered around the wand. "Not sure. I'll have to look at it closer whe –"
A small sound from above cut him off. They all turned to face the rafters, only to realize the sound was coming from higher up the staircase.
"Mrs. Norris!" Lindsay exclaimed. "Filch is coming!"
Sherlock dropped from the wall with surprising agility, landing in a half crouch that set him in an excellent position to run. John had already bolted down the steps. It took him three turns in the stairwell to realize the others were not at his heels or passing him. He glanced back to see Sherlock saying something to Lindsay as they trotted along. She nodded and bolted back around the corner. Sherlock caught up with John in three long strides and pulled him along.
"Where's Lindsay going?" John asked, skidding to a halt.
"She's coming, I swear. Now go!" Sherlock snapped, grabbing John's arm and yanking.
John planted his feet just in time to see Lindsay barreling around the corner.
"Go on!" She snapped in an undertone, galloping past them both and heading for the corridor, robes billowing behind her. Another, uneven set of footsteps from above sent the boys after her.
Sherlock regained the lead just in time to duck through a door pretending to be solid wall onto a little-used staircase that led up to the fourth floor. From there they took a chance on the main stairs. Filch was nowhere to be seen above or below. Sherlock, still in the lead, sent a freezing charm at the moving staircase, stopping it at the landing they needed. They dashed up and waited just long enough for Sherlock to freeze the next two sets of stairs, which lead them up to the seventh floor.
They arrived on the landing of Gryffindor corridor, breathless, laughing, and unfollowed. Sherlock pulled his shoes from inside his robes and slipped them back on. John leaned against the wall, gulping at the air. He'd done his best to rebuild his stamina since the weeks spent in hospital, but he wasn't quite up to a sprint across the castle. His leg would never forgive him.
His cane. "I've left my cane on the stairs," John exclaimed, bolting up from the wall.
Lindsay and Sherlock exchanged a look, still chuckling. It took a moment for them to focus back on him and read the askance look on his face.
"Did you miss it?" Lindsay asked.
John spouted the beginning syllables of several sentences before settling on, "That was adrenaline. Fight or flight, or some such."
"How about now?" Sherlock offered. He tossed the vial he'd gathered at John, but far to the right.
John sidestepped instinctively to catch it, landing with all his weight on the leg that had refused to support him since May. He half-braced himself, but the knee didn't buckle and the muscles felt as solid as – as they had before the battle. During the battle, too, if he was honest. A slow, reluctant grin fought itself free from his tense facial muscles. He tossed the vial back to Sherlock, who caught it with a cat-like controlled swipe and laughed again.
"Just proving a point."
"But my cane," John said, suddenly sober. "Filch will have found it."
Lindsay pulled it from within her robes. "Sherlock told me to go back for it."
John took it, hefting it slightly from hand to hand. It already felt like an unwelcome intrusion. He turned down the hallway. "Well, then. Do you think Madam Pomfrey will release me for the Quidditch tryouts?
The Fat Lady interrupted before either of them could answer. "What mischief have you been up to?" she demanded with none of her usual conspiratorial tone.
The three stared at one another, groping for an explanation, when the portrait hole swung open and an ink-bespattered Professor Smith stepped out. He folded his arms and stared at them, an effect which was somewhat spoiled by the large smear of ink above his eyebrows which gave him the look of having a uni-brow above the real ones.
"Any explanation?" he asked..
John ran through the options in his mind. The truth was out of the question, and any lie too far-fetched to make believable. He glanced over at the other two. Sherlock had drawn breath to speak three times, then stopped himself.
"Alright then," Smith said. "Detention. My office, Saturday morning, 9 a.m."
"But, sir," Lindsay blurted, looking a bit surprised at her own daring. "It's quidditch tryouts Saturday morning."
Smith seemed to consider. "I suppose I ought to make you come anyway, giving up a pleasure and all that…" he grinned, showing off an ink splatter that had managed to black a couple of teeth. "But I want a stupendous Gryffindor team. So go on to the tryouts. Let's make the detention 2 o'clock instead."
They all muttered their thanks, and Sherlock turned away to the Ravenclaw dormitory looking only slightly murderous.
"Oh, Watson, Lovejoy," Smith said, turning on his heel at the stairs. "Peeves is still in there. Nip him out before you go to bed, won't you?"