Author's Notes:This will be a full length AU fic and will be posted up here as I finish and my lovely, amazing beta, kathecello, cleans them up! Warnings for the whole story: general adult themes, swearing, mentions of child abuse, violence and graphic sex. Rating has gone up.

So big news this chapter! The How to Build a Heart out of Ashes blog is now up and running with a few nice posts up already. Including the first of three fanmixes and a very lovely piece of fanart. I hope all of you have some fun with it! The url (if you take out the spaces) is "heartoutofashes . tumblr . com . Thank you all SO much for your reviews. Each one of you brighten my day =]
PS- Why does ff . net always have to go down when I am trying to post? Sorry for the delay and possible multiple alerts!

How to Build a Heart out of Ashes: Sparks

by: Teumessian

For a dance that was being held in a gymnasium, the student council and staff had really outdone themselves. The walls were covered in black and grey draperies. Gorgeous arrangements of silver were scattered all about the room. A large buffet table sat along one wall; platters of sweets and snacks sat on a black table top. The DJ and his tables were perched on a raised platform at the back of the gym. There were already a number of couples on the dance floor. A few sparkling disco balls, that would most likely be put to full use later in the night when they turned down the lights, hung from the ceiling. There was obviously a large range of ages in the attending students. There were numerous awkward secondary school couples. Groups of girls, dateless but seemingly enjoying themselves all the same, twittered about on the edge of the dance floor. Relaxed university couples seemed to be taking pleasure in the scene and the food and there were even a few blokes who decided to go stag leaning against the far wall, apparently trying to influence the DJ.

Having arrived together only a few minutes previously, John Watson stood with his friends next to a pillar close to the entrance of the gym. He wore a simple black suit with very faint pinstripes that he had bought for the wedding of his uncle last winter. Harry had made fun of him for accidentally getting pinstripes but his measurements had already been taken for the suit and the thought of going through the process again had made him balk. In the end they looked rather good on him anyway, he thought, and the suit contrasted nicely with the pale blue shirt he was wearing to match Sarah's periwinkle dress. With the addition of a simple charcoal grey tie and a touch of product in his hair, for once John actually felt he did a fine job of making himself more than presentable.

Molly looked lovely in a yellow satin dress, sweetheart neckline and floral stitching climbing up from the hem. John was not the only one to do a double take at 'unassuming' Molly Hooper that evening. Greg was being a great date and looked rather dashing himself. Mike was accompanied by a sweet girl with curly red hair and dimples, Suzie from his psychology lecture.

John scanned the crowd and regularly glanced over at the wide open doors and the constant influx of arriving couples. Sarah glanced up at him.

"Sherlock is coming separately, right?" she asked.

"Yeah, with that Adler woman," John murmured.

If he hadn't been glancing at the door once more he would have seen the little smile pass over Sarah's face at his phrasing.

Even before a few weeks ago when Sherlock announced her as his date, John had heard about Irene Adler. There were very, very few who hadn't, but for whatever reason the rumours and school legends seemed to be reaching John at a surprising rate in the recent days. He had no idea how much of it was true, but if one tenth of the stories were true then Irene Adler was a more fearsome woman than any John had, or probably ever would, meet. There was a reason she was called 'the Vixen' in the whispers of story tellers, and her fox shift was not the biggest reason.

He'd known that Sherlock and Irene had an odd sort of relationship. It wasn't exactly a friendship. As far as John could tell, Sherlock only ever seemed irritated by her presence but he had to admit Sherlock didn't dismiss her like he did to everyone else, besides John himself at least. From what he'd heard, Irene had been an extremely young Change herself. She'd been at the Institute since she was seven and since she was a year older than Sherlock, that meant she'd been at the Institute almost as long as Sherlock had. Apparently even Sherlock could be won over to some degree with persistence…

John was watching a couple of sixth formers compete to see how many biscuits they could fit in their mouths at one time, so he wasn't looking at the door when the conversation of his friends trailed to a stop. John glanced at them to see them all staring in the same direction. Sarah followed their gaze first.

"Oh… wow…" she breathed, and John's head twisted towards the door.

Then he had to admit some of his own breath slipped through his lips because Sherlock Holmes and Irene Adler had arrived and that was certainly a sight to see.

Irene was encased in a silken, purple, formfitting number with an asymmetrical hem and strappy black heels that could easily put your eye out. She wore a beaded necklace that looked like lace from across the room, and even from there, John could see her eyes were painted into wickedness. She looked more beautiful and dangerous than anyone John had seen in his short life. The Vixen, indeed.

Then there was Sherlock, and here was the strange part, he wasn't outshone by her in the slightest. He not only was recognizable but he was in balance with her, in his tailored black suit, beautifully cut, buttons gleaming and wrapped in a silk shirt that matched the shade of Irene's dress perfectly, his glossy curls paired with the lace curling around her neck and chest.

Irene was smiling smoothly and Sherlock looked like ice and with a strange hot swoop in John's stomach he realized they were perfect—so goddamn perfect. Where was his dorky, socially inept best friend? Where was Sherlock, hands covered in vegetation in the name of science, smiling at John's praise? But no this was truly Sherlock, in every way. Sherlock perfected…

Then eyes found him, steel grey and piercing. They held for a moment across the crowd but then for some reason John found himself looking away, insides doing strange, almost painful things. What the hell? Sarah glanced up at him.

"Do you want to dance now? The floor is filling out," she nodded towards the rapidly filling dance floor.

John swallowed and forced a smile.

"Yeah, sounds great," he said.

. . .

Irene had stopped by earlier that evening to drop off the shirt she'd wanted him to wear. It was the same colour as a shirt he already owned, he pointed out, but Irene had said that this material was better, so he'd agreed to wear it if only to get her to leave him alone. The woman had commented on his particularly foul mood today, but he'd elected not to indulge her with a response. Sherlock was lucky to have the suit already, a relic from the few birthday and garden parties that he had been convinced—blackmailed—into attending over the past few years. It fit him well and he did like it in all honesty, but today he had just been feeling a distinct lack of motivation to put any effort into the evening at all. He had certainly second guessed the reasons why he'd agreed to go in the first place, if he could even put a finger on what those reasons were. But then the image of John twirling around a pretty blonde girl would enter his mind unannounced and by coincidence the urge to attend the silly school function returned as well.

So this was how Sherlock could be found leaning against the far wall of the decorated school gymnasium, behind the speakers so his eardrums weren't permanently destroyed. Irene leaned in beside him.

"Come now, Sherlock," she purred. "What have I told you about scowling?"

Sherlock just scoffed and rolled his eyes, continuing to watch the pulsing crowd, trying to convince himself he could learn something here but there was nothing he didn't already know.

Except for a brief greeting in passing, Sherlock hadn't talked to John. He had however caught glimpses of him dancing with Sarah in the crowd. He seemed to be having a fine time. Sherlock even saw him laughing as he danced a song with Molly. It was sickeningly mundane.

It was so loud, voices, bad music and incessant laughter clanging against his mind. He wished he was out in the forest, in the quiet shadows, only one voice ever reaching him there.

A hand slipping into his broke his focus on his fantasy and his fingers spasmed in surprise and his head snapped down.

"What are you doing?" he asked, annoyed, as Irene started to pull him towards the chaos.

Irene sent him a half lidded glance over her shoulder.

"It's a dance, Sherlock. I hardly asked you here for enlightening conversation," she chastised teasingly, making Sherlock bristle.

But then the crowd parted a bit and Sherlock saw John spinning Sarah around in a cheesy twirl that made him want to be sick and he found himself snaking his arm around Irene's curved waist. Then they danced.

Sherlock had no particular feelings positively or negatively regarding dancing but he was a great mimic and so some relaxed easy form of dancing was easy, and he mostly ignored the more ridiculous and flamboyant displays put on by his fellow students. Irene was mostly leading anyway so it was easy to slip back into the quieter place in his mind.

Sherlock wasn't sure how long this had been going on when the attention light flickered on in his brain and he immediately began to look for what had set it off. Two and a half seconds later he figured it out. It was the small boy standing pointedly next to the open doors. Primary students weren't allowed at the ball, plus Sherlock not only recognized the boy but he was staring straight at him. With his next heart's beat, a chemical dose known as excitement flooded his body. Oh, yes, this could only mean one thing.

Irene had noticed the shift in him and was watching Sherlock closely now, especially at the gleeful smile that had broken onto his face and then he leaned in close to whisper in her ear.

"I apologize but it seems I am going to be otherwise engaged for the rest of the night."

. . .

John forced himself to at least seem like he was having fun. Despite his old friends' jokes, John's past luck with women had not been because he simply 'had game.' Even if deep down he did really hope to get a glimpse of their knickers at some point, John was raised to treat women properly. So even though John was having far less fun than he expected, he did his best to make sure Sarah and his friends got the most out of the night, and he had genuinely enjoyed dancing with both Sarah and Molly, who he and Greg seemed to be reaching some success in getting her to cut loose.

The DJ had started a slow dance and currently Sarah's arms were wrapped completely around his neck, his around her lower back. They were very close as they swayed back and forth. This should have made John feel elated. On another night, in his old life, he would have taken this as a positive sign that this night could end in some very satisfying snogging if he played his cards right, but he would be damned if there wasn't something wrong with the way Sherlock Holmes swayed with an absolutely gorgeous, highly experienced woman plastered all up his front.

I mean how did she even do that? It had to be impossible to wrap yourself so completely around someone, outside of the bedroom at least. That brought on a whole wave of related images that turned John's cheeks pink. He wasn't so inexperienced himself but he was not thinking about Sherlock in Irene Adler's bed. His brain couldn't handle it.

That was it! That had to be why it was bothering him so much. This wasn't Sherlock. It just didn't fit. Irene would just be using Sherlock and that was not tolerable. Not with the knowledge of Sherlock's past firmly resident in John's mind. In his head John carefully labelled these facts as 'reasons' and not justifications for his feelings as he decidedly spun Sarah and himself so his back was to the figures he couldn't divert his attention from.

After a long stretch of dancing John gave in and craned his head to catch sight of Sherlock again, to make sure Irene wasn't taking advantage of him of course. He caught sight of the Vixen, leaning against the wall with a glass of punch in her hand, but there was no sight of Sherlock. Strange. He started to grow concerned but then a popular song came on and the whole group's excitement rose palpably. Greg whooped and pulled Molly into a twirl and Mike and Suzie were doing some odd dance that apparently went with the song. John couldn't help but laugh. Only when the song was almost over did John become aware of Sherlock's presence. This was because the Changeling was right behind him.

"John!" a voice cut through the music and John spun around to see his best friend not a metre away.

His eyes were crackling with excitement. John's concern flared again.

"What is it, Sherlock? Everything okay?" John said, voice almost drowned out in the thudding bass of the pop song.

"It's happened again—maybe! We have to go now," Sherlock said, visibly rocking onto is toes in eagerness.

His friends were watching now.

"What?" John asked, confused as usual.

Sherlock looked highly impatient and his hands fluttered around.

"Another Wandering, John! Come on!"

John was still lost and it was hard to explain anything in the din.

"What?" John asked and Sherlock's patience visibly expired.

"Oh, I'll just explain on the way! Come on!"

Then Sherlock reached forward and grabbed his wrist with long, thin fingers and began to pull him towards the exit.

"Wh-what are you doing? Wait—Sherlock!"

John protested but Sherlock ignored him and didn't let go. He only managed one glance back at his friends who, unlike John, didn't even look that surprised at all.

A moment later Molly came up next to Sarah.
"I'm sorry," she apologized for Sarah's absent date.

Sarah just laughed and shrugged.

"It's okay. Who is surprised? Just out of curiosity, though… I know you're friends with them, do you know what… is up with those two?" she asked, not sure how to phrase the question but Molly knew exactly what she was asking.

"I'm not really sure, exactly. Nobody really is, them probably least of all, but… they do have an open bond," Molly said, explaining at least a part of it.

Sarah's head snapped around at Molly's last words, hair brushing against her bare shoulders.

"You're joking," she said, eyes wide.

Molly just smiled softly and shook her head. Sarah giggled.

"Well, I had even less of a chance than I thought," Sarah laughed. "How do you compete with that?"

The look on Molly's face said she understood the feeling perfectly.

With a sigh and a smile Sarah stretched her neck and glanced over at Molly.

"Well, the night's not over yet, is it?" Sarah said, nodding towards the moving bodies.

At that Molly's smile returned as well.

"Oh, I hope not."

Across the dance, another young woman watched the exchange and departure of Sherlock Holmes and John Watson. Once they were surely gone a vulpine smile bloomed on her face. This night hadn't gone exactly as it had been planned but oh, it had gone somewhere and that was something—something interesting and surely important. With graceful, polished fingers, Irene Adler extracted her phone from her recovered clutch, and then she began to send a text.

. . .

"Seriously, Sherlock, what is going on?" John asked as Sherlock led them into the hallway.

"Another student has Wandered. If there's something strange about this one I want to find it before the evidence disappears," Sherlock said as they approached a small shape at the end of the hallway. "John give me the tenner in your pocket."

Would John ever be able to keep up with this boy? They came to a stop in front of the small shape, which turned out to be a primary student. He didn't look older than nine years of age.

"I—ah," John said eloquently as Sherlock stuck out his hand demandingly.

He reached into the pocket he'd stuffed a few notes into, just in case, before he'd left his room that evening. He didn't question how Sherlock knew it was there, but that was not very high on his list of priorities at the moment. He handed Sherlock the tenner and he immediately tucked it into the waiting hands of the little boy who immediately scampered off. Then Sherlock began to lead them in the opposite direction.

"Okay, still lost," John said irritably. The Changeling was impossible when he was distracted like this. "For the stupid people in the room, would you please explain what going on—preferably from the beginning and who was that boy?"

Sherlock sighed heavily as they turned around another corner.

"Lucy Heart, John! Or had you forgotten?" he said.

John did remember Lucy Heart, the girl that had Wandered last spring, the girl who Sherlock believed hadn't wandered at all.

"I remember," John confirmed.

"Well, when nobody took the facts into any consideration last time I realized I would need more evidence, so I set up for the possibility of the event reoccurring. That boy was Adam Knight, one of the many primary students who gather information for me. I instructed them to alert me the moment they heard about a Wandering, so I could investigate its validity."

John's eyebrows furrowed and he looked up at Sherlock.

"Wait, you have primary students collecting information for you?"

Sherlock smirked back at him.

"Oh, John, you would be shocked with how much is said around children under the misguided belief in their lack of understanding or ability to retain useful information, especially under the incentive of sufficient money to buy enough sweets to get sick on."

John thought that over for a moment, twin footsteps echoing loudly in the dark corridor.

"Okay," he acquiesced. "So someone has Wandered again?"

Sherlock nodded sharply.

"Justin Hara; disappeared this morning. He was supposed to attend a pre-ball function but he never showed up. The staff found his things in a Changing booth and they found no sign of him in their sweep of Baker Forest. He was a komodo dragon shift… neat, yeah?"

John's eyebrows rose and he understood Sherlock's interest. Changelings were most commonly mammal shifts, followed closely by avian shifts, then marsupials, then, very rarely, reptiles. For whatever reason, there were no fish or bug shifts. Some scientists said they were perhaps too different from humans to be one with them, but either way a reptile shift was unique and to be such a rare species on top of that made it doubly so.

"Okay, makes sense," John said, finally catching up. "So where are we going?"

John's voice was conversational and some part of him was wondering why he wasn't more upset that Sherlock had pulled him out of the middle of the dance, making him leave Sarah dateless.

"If we want to find anything out of the ordinary we have to do so before it disappears. We are going to check his changing booth."

About twenty minutes later, John had shed both his fancy clothes as well as his human skin and was nose to the earth in front of the booth were Justin Hara had made his last shift. Sherlock was inside the booth, mouth open and drawing in air. John knew he did this when he was trying smell something faint.

Find anything? John asked.

Irritation. All I can really smell is the human in here, from when they collected his things. My sense of smell isn't as good as yours. Sherlock said begrudgingly, which made John smile inwardly. Is there anything out there?

John sat back and scratched his ear.

Not that I can smell. It rained this afternoon, though. Even if there was anything it would probably be washed away by now.

Disappointment. Come try in here. Sherlock instructed and padded out onto the grass to give him room.

They'd pushed back the curtain so it was easy for John to cross into the sheltered room. He glued his nose to the ground and started sniffing. Sherlock was right, the smell was indeed primarily human, but John could also smell more, many faint Changing scents, most over a day old. Then he picked out an odd scent—reptilian. That must have been Justin's, but there was one other, fresher, scent. It was faint but surely a mammalian smell—not human. He told all of this to Sherlock, who was watching, patiently for him, from the grass.

At first the panther said nothing, and John was about to ask when Sherlock stood.

Fancy a run? he finally asked simply.

John's ears twitched then he rolled his shoulders. He'd already ruined the evening and he didn't feel like going back to the dance anyway—in fact, until that moment he'd actually sort of forgotten about it.

Sounds good. John said, slinking after the dark shape, knowing it was pointless to try and get answers out of Sherlock if he wasn't offering them.

Don't speak. I need to think. was all Sherlock said as they passed the tree line.

John rolled his eyes but he did stay silent.

. . .

The next night John received a text requesting his presence in Baker Hall. He took one look at his unfinished maths coursework and stood with a sigh, shutting off his desk lamp. A few minutes later found John standing with his hands stuffed into his coat pockets in front of the huge black doors of Baker Grand Hall. At this hour the door should have been locked but John was rather unsurprised when the door swung open on his first attempt.

Once inside he looked around the gloom, even in the darkness John quickly picked out the shadow standing close to the far corridor, staring at the wall. John approached and when he got close enough to speak quietly and be heard, he greeted Sherlock.

"How did you get in here?" John asked.

Sherlock didn't look away from the wall—the Wanderer's Wall. He just held up a set of keys that jingled louder than John liked.

"Jesus, Sherlock, are those Greg's?" John said, grievously.

Sherlock just nodded and leaned forward to study the newest addition to the wall, Justin Hara. His purple marker hung below his pictures. So he'd been a secondary student.

John mentally promised himself he'd have Greg's keys back to him by morning and dismissed his concern for later.

"So why did you need me to join you in this break in?" John asked.

"I need you to shift," Sherlock said simply.

John said nothing. Then Sherlock's words sunk in.

"In here? No—why?"

Sherlock glared at him over his shoulder.

"Because, John, this is actually Justin's marker, not a replacement. Wear is consisted with use on the outside, and the inside shows it was worn by something with scaled skin."

John pursed his lips, trying to catch up, arms crossed over his chest.

"So… this was a normal Wandering? Why do I have to shift?"

Sherlock made a dismissive motion with his hand.

"Maybe—or maybe someone knew a missing marker would be noticed this time as it was last time," Sherlock hissed at John's slowness. "I already shifted and tried gleaning something from the smell but again, I can't get anything but human off of it. I need you to check."

"But—but I'd have to…"

John's ears were red and he was acutely aware of their presence in a place that normally saw hundreds of bodies passing through it constantly, not at all private. Sherlock shot him another despairing glance.

"I'll face the wall to protect your fragile decency. Just do it," Sherlock said.

John only hesitated a moment more before sighing heavily and turning around.

"Fine," he said.

He quickly undressed; shooting a glance over his shoulder to make sure Sherlock was still firmly facing the wall before removing his pants. He didn't know why he was being such a prude. It's not like he hadn't undressed in front of blokes in locker rooms for years.

Once he was clothed in thick blonde fur he relaxed. He turned and padded towards Sherlock as well as Justin's memorial. When he was close, he bumped his muzzle against Sherlock's leg, telling him to move.

This was the first time they'd been like this, John shifted and Sherlock human, but just as it hadn't really bothered him on the night Sherlock slip-shifted, the dynamic didn't really change, nor was communication very hindered. It seemed when it came to them that nothing was dependent on exactly how much hair, or how many feet, claws or tails they had.

Once he was centred, John reared back, blunt nails clicking loudly against the wall as he propped himself up with his paws. From this position he could press his nose to the leather marker. Almost immediately, Sherlock spoke.

"What do you smell? Focus on the—"

Sherlock cut off when John narrowed his eyes in the young genius's direction.

Calm down, I'm working on it, the glance easily conveyed.

John went back to the marker and inhaled. The strongest scent was definitely reptile this time. This was obviously Justin Hara's marker. The next most prominent were the humans who had handled it after he Wandered. John was about to conclude his assessment but then he realized there was another scent. He pulled away to clear his nasal cavity and began snuffling over the entirety of the purple leather. He finally figured it out when he passed over a spot where the scent was stronger. It was the same mammalian scent he'd encountered in the changing booth.

With a curious cock of his head, John dropped back down to the tiled floor.

"What is it?" Sherlock asked, curiosity eating him alive as it was obvious to him that John had found something.

John flicked his muzzle towards the wall and walked towards his clothes. Sherlock complied and turned towards the wall. By the time John was clothed, Sherlock was bouncing lightly on the balls of his feet.

"It's the same as the booth," John said and Sherlock whipped around, striding over to him, encroaching on personal space.

"How exactly do you mean? It is vitally important, John," Sherlock said, eyes painfully intense as he leaned over John, whose eyebrows furrowed in concentration.

"Well, it's definitely Hara's marker. It smells mostly like the people who retrieved it, but there's that same faint non-human mammal smell there, too. Mostly on the one side," John explained, indicating the top left side.

Sherlock spun away in an instant, arms flying up.

"Brilliant!" he exulted, spinning in a full circle.

John was officially lost but he was fairly sure it wasn't socially acceptable to be this excited about whatever it was.

"What? What does it mean, Sherlock?"

Sherlock turned and grabbed both John's shoulders, looking straight into his eyes. John was a little overwhelmed by the excited light in his eyes.

"It means, John, that something carried that marker back from the forest. It means he was wearing it! He was wearinghis marker when it happened, John! Something Wanderers never do! Just the same as Lucy Heart. But they—it—knows the marker was missed last time so they brought it back!"

John shook his head and shut his eyes for a moment so he could think properly.

"Wait—wearing it when what happened?" he asked.

Sherlock smiled like a mad man.

"When he was taken, John. I don't know how, and I don't know why, but someone took Lucy Heart and Justin Hara and tried to make them look like Wanderings. And if I'm right, they won't be the last."