A/N
A Mortal Instruments AU written for theawesomeme-willmoveforward as part of the PrUK Secret Santa 2015

Fated Encounter

The boy opened the heavy spellbook, his green eyes flicking fervently over the words on the yellowing pages. He'd always seen things he shouldn't have had, beings with unnatural skin colours and eyes, or with wings, claws, hooves, tails and horns, occasional dreams and visions of the future. He'd long learnt not to speak of them, his friends and classmates had called him crazy and began to avoid him, and his parents exchanged concerned looks before blaming his imagination, saying it would go away. Or so they'd hoped and he'd let them believe. He'd found the book in the attic and now he'd use it to prove the supernatural existed, that he wasn't crazy. Tracing the diagram on the page onto the floor, he began to recite the spell he'd chosen, tongue stumbling slightly over the Latin words. Feeling something stir within him, he smiled grimly and waited for the spell to take hold.

The view from the roof of the London Institute was incredible, even Gilbert Beilschmidt had to admit that. The seventeen year old Shadowhunter was under the spire of the Institute, one of his usual haunts, having climbed to the roof from out of the attic window. The breeze ruffling through his unkempt hair, Gilbert exhaled sharply, wondering how long it would be until he was sent to yet another Institute. It wasn't as if he'd done anything wrong this time, but both Berlin and New York had found him too troublesome for them to handle. He remembered first arriving in New York, aged thirteen, his parents having decided he would be a bad influence on his younger brother Ludwig if they stayed in the same home. His family was old, but not rich or all that influential until lately, when his father became the head of the Berlin Institute after the Dark War. He'd contacted Maryse Lightwood and arranged for Gilbert to be trained at the New York institute instead. The two years he'd spent in New York hadn't been all too bad, between meeting the famous Jace Herondale and causing trouble at the High Warlock Magnus Bane's parties, he'd had rather good time. However the trouble he caused – alongside fellow Shadowhunters, he might argue – did not go unnoticed and disapproved of. Without the immunity of being a hero of the Dark War, he was punished by being sent away, yet again, this time to London.

'Hej, I knew I'd find you up here,'

Gilbert didn't have to look in the direction of the familiar voice that pulled him out of his reverie to know it was Matthias Køhler. He turned around and smiled crookedly at his parabatai, who was also a ward of the London Institute.

'You know me too well,' he retorted, smile not faltering. 'Come to tell me off for brooding?'

Matthias punched him lightly on the shoulder.

'As much as I'd like to tell you that's the case,' he said with his trademark wide grin. 'It isn't.'

His expression sobered slightly, and he took a moment to peer out over London, seeming to search for something.

'Somewhere out there,' he said finally, gesturing out at the city beneath them. 'Someone summoned a demon, an anonymous Downworlder source just sent a message to the Institute, and we're supposed to investigate.'

Gilbert whistled, taking in the information.

'So either it's bad blood between Downworlders or someone inexperienced has set a demon loose,'

'Either way, Downworlders are involved,'

'You never know, it could have been a mundie,' Gilbert snickered at the seemingly impossible eventuality, brushing past Matthias to climb back down through the window.

'A dead mundane, in that case,' Matthias pointed out as he followed Gilbert back inside.

The boy's name was Arthur Kirkland, and he had made a mistake. As soon as the circle began to glow, he noticed it. The circle was not complete, one of the chalked runes on the floor was broken. He swallowed, recoiling as the beast appeared, the maggot like body with its mouth full of razor sharp teeth and the spiked arms protruding from it. The air filled with a repugnant scent as the fleshy beast thrashed against the protective circle, making a menacing clicking noise as it did. Arthur figured it would not be long until all of the runes failed and the circle couldn't protect him any longer. Scrambling away from the thing he had summoned, Arthur tucked the spellbook under his arm and ran, not looking behind him until he reached his bedroom. Slamming the door shut and chalking what he hoped was a barricading spell upon the door, he grabbed a pair of scissors as a weapon and began to flick through the yellowed pages again, trying to find something to protect himself with. He could already hear clicking on the stairs, and shuddered to think the cumbersome beast could move that fast.

Having Marked each other with runes for enhanced speed and vision, glamoured and armed themselves with steles and seraph blades, the two Shadowhunters made their way to the address mentioned in the tip off. As they approached, Gilbert raised his eyebrows at the sight. The area they were in was not one that many Downworlders took up residence in, and the house in question lacked glamour and any other sign it was anything out of the ordinary.

'Maybe I was right about it being a mundie after all,' Gilbert muttered, although he'd never actually believed it wasn't a Downworlder's doing.

'A dead mudane,' Matthias corrected, shaking his head at the slang his parabatai had picked up in New York.

Gilbert snorted but didn't reply, scrunching up his nose as they reached the front door. The Sensor he was holding vibrated violently, but the stench of rotten garbage issuing from inside was enough evidence of a demon being present.

'A Drevak by the smell of it,' he commented, giving Matthias an idle smirk. 'It should be easy enough to deal with.'

Pocketing the Sensor, he prepared to kick open the door, only to have Matthias brush him aside and trace the opening rune onto the wood with his stele.

'You don't have to rely on brute strength all the time you know,'

'I know, but it's fun to kick doors down,'

Matthias laughed lightly.

'Of course you would say that,' he muttered. 'But as you said, this is a mundane house, and it would just be a little suspicious if there was a bad smell and a broken door, don't you think?'

'Oh whatever, you kicked the door down on the last investigation we did,'

'Yeah, yeah but that belonged to a warlock,'

'Fair enough, let's just go get that stinking demon,'

Matthias decided against asking if that was a terrible pun, knowing Gilbert, it probably was.

The house was immaculate, save for the kitchen where there was a circle of runes drawn on the floor. Both Shadowhunters were experienced enough to spot the flawed rune immediately, instantly recognising it as what had been the weak link in the circle.

'It's rare for mundanes nowadays to know about the Shadow World, let alone get involved in magic,' Matthias remarked, looking sombrely at the ruined circle. 'Poor person probably thought they would get wealth and fame, but instead they just got eaten.'

'That's unusually grim for you, Matthias,' Gilbert replied, though his skin did prickle at the thought of what must have happened to the mundane.

Leaving the kitchen, they noticed the smell was stronger by the staircase. Matthias shared a glance with Gilbert before they both ran up, silently, two steps at a time. The sight that greeted their eyes when they reached the top was indeed a Drevak demon. For whatever reason the bloated larval creature had not noticed them. It was facing one of the doors, seeming to be trying to find a way past the wooden barrier.

'You want the honours?' Matthias nodded at Gilbert, tilting his head at the demon.

'Sure,' Gilbert replied, lazily drawing a seraph blade.

'Araquiel,' he intoned in an almost casual manner, the blade springing into life as he named it.

By this time the demon had noticed them, but before it even fully turned around, Gilbert had thrown his blade at it. The blade arced through the air, catching in the light as it did, finding its mark in the Drevak demon's gaping maw. The beast froze, then promptly exploded into a cloud of dust. As the dust settled, Gilbert walked into it, grimacing as it got onto his boots and retrieved the blade. Wiping the dust on the blade onto his shirt, he turned around to face Matthias.

'That was a real messy one,' He said grinning, getting dust onto his face as he ran a hand through his hair.

'Yes, and nice shot,' Matthias snickered, rolling his eyes, pre-empting what his parabatai would say next. 'Now let's go and get some food.'

Gilbert furrowed his brow, something that Matthias didn't think was possible when food was mentioned.

'You go first,' he said, looking at the door the demon had been trying get through. 'I want to check something out first.'

His sensor wasn't reacting to anything, so there was nothing particularly threatening behind the door, but his instincts told him there was something there worth investigating. After all, even a demon as unintelligent as a Drevak, would not had been so focused on something that it had missed the presence of two Shadowhunters entirely for no good reason.

'Alright,' Matthias replied with a laugh, assuming Gilbert was just being pedantic. 'I'll see you at that place near St James's Park.'

Gilbert nodded, already testing the handle on the door. Locked. But there was something that felt…unusual; out of place about it. Taking Matthias's advice from earlier, he traced an opening rune on the door and felt it budge as he pushed it.

Arthur had given up on finding a spell to combat the demon, figuring it would not be smart enough to get in before he managed to climb out of the house, when he heard voices outside his room. He was fairly certain he hadn't read any of the spells out loud, but couldn't be sure. What if he'd accidentally managed to summon more demons, one more intelligent than the beast he'd initially summoned. Abandoning the sheets he was tying into a rope, his gaze darted from the door, to the scissors to the book as the handle rattled. Eventually deciding the book would be a more durable and hefty weapon, he picked it up and stood just beside the door on the side it opened on ready to unleash his makeshift weapon on whatever opened the door. He did not expect to drop the book in shock of recognition when the door did open however.

"Well Matthias will be surprised when I tell him the mundie isn't dead" probably was not one of the smartest thing Gilbert had ever said when the green eyed boy dropped a heavy tome almost onto his feet. Never one to be set back by his own words, he continued:

'So you're the one who summoned the Drevak demon,' he spoke conversationally, as if he was just talking about a day to day event.

Having decided to take the glare he received as a "yes", he also decided to not comment about how the other boy's eyebrows were much darker than his hair, seeing as he must have had a pretty rough day already.

'Shoddy job there with the runes. It's a miracle you didn't get eaten.'

He scanned the room, snorting slightly at the pile of bed sheets on the floor and completely missing the look of concentration the mundane had as he stared at Gilbert.

'I know you from somewhere,'

The sudden accusatory tone cased Gilbert to pause in his observation of the room in order to give the other boy a sardonic look.

'I highly doubt that,' he said in a self assured tone, having always been in glamour while in public, not realising he'd never dropped the invisibility glamour he'd put on before he and Matthias left the Institute.

'Well I have,' the boy persisted stubbornly, his eyes then widened fractionally as he remembered where he'd seen the striking features before. 'You were in my dreams.'

'Well that's a line I haven't heard used on me before,' Gilbert muttered absently in response, once again scanning the room and ignoring the disgusted noise of frustration the mundane made.

'Wait,' he spoke intensely as his eyes focused on the runes on the door. Holding. Protection. Strength. Coming to the realisation he was supposed to be invisible to mundanes as well. 'You were serious, weren't you? What was your name again?'

'I never told you my name,' came the terse reply. 'You barged into here without invitation and just started making assumptions.'

Gilbert could tell the boy was getting riled up and quickly cut him off.

'That doesn't matter, you shouldn't even be able to see me. Just tell me your name.'

The mundane looked incredulously at him through narrowed eyes for a few moments.

'It's Arthur,' he finally muttered through gritted teeth. 'Why is my name so important anyway?'

Gilbert shook his head, dismissing the question.

'That doesn't tell me anything, what's your surname?'

'Kirkland. What else do you want to know about me?' The boy spat out the question after another glare.

But Gilbert had stopped listening after the first word, now it was his turn to stare.

'That's the name of one of the most famous Sighted families, but the last living members disappeared almost half a century ago,' he said bemusedly. 'It can't just be a coincidence that you have the Sight and clairvoyance as well.'

Seeing Arthur's flabbergasted expression, he sighed, already seeing a picture of what had happened to the family.

'You don't know anything about the Shadow World, do you?' He took the blank look he received as a "no".

'Well it's technically against the Covenant to tell you, but you're technically not a normal mundane… So brace yourself.'

Over the next half hour, Gilbert relayed in abbreviated detail, Shadowhunter history from Jonathan Shadowhunter to the Dark War. Paying particular attention on filling in Arthur on his family's history.

'So basically,' he concluded. 'We're a bit short of Shadowhunters after that little incident with everyone getting corrupted, and Sighted mundanes, especially ones of your family's calibre are perfect for filling in the ranks, or so to speak.'

Gilbert grinned, hoping to have convinced Arthur. In his reasoning, anyone who managed to summon a demon and survive without having any real knowledge of the Shadow World was worth getting to know and even be friends with.

'So this is the Ascension thing you talked about?' Arthur asked raising an eyebrow.

'Hey so you did pay attention— I mean yes, that's exactly what I was talking about,' Gilbert watched the mundane expectantly, feeling a mixture of hope and excitement. 'Does this mean you'll come with me to the Institute?'

'And I'll have to go study at the Academy?'

'Well, yes, but I visit there occasionally,' Gilbert shrugged, not knowing why he'd said that. After all it was half a lie, he'd only visited the Academy once with Jace Herondale while he was still studying in New York.

Arthur seemed convinced though, and he decided to broach onto one last problem.

'Your parents—'

He didn't expect to be interrupted.

'Knew about the Shadow World,' Arthur said with conviction. 'I'm sure of it; they weren't surprised when they realised I had the Sight.'

'You do realise that they disappeared from the Shadow World for a reason then; they must not have wanted you involved,' Gilbert was not trying to discourage Arthur, quite the opposite in fact, but from what he'd gleaned about the mundane boy, this was the kind of encouragement he need.

Arthur crossed his arms.

'They should let me decide that for myself,' he declared stubbornly, which was precisely the reaction Gilbert had hoped to achieve. 'I'm going with you to this Institute or whatever you called it.'

'Are you sure?' Gilbert asked just to be annoying.

'Of course I am,' the retort was instant as Arthur opened the door and crinkled his nose at the pile of dust outside his room. 'How hard can this be?'

'There's always the risk of dying at Ascension,' Gilbert reminded him, miffed at the almost cockiness.

He regretted saying that instantly, even if it was true. Fear flashed briefly through Arthur's eyes before he recomposed himself.

'Well I won't,' the green gaze was steely and Gilbert found himself believing the words even if it was still an uncertainty. 'You said it was easier if the candidate wasn't an adult and I haven't turned eighteen yet.'

So they were the same age, or around the same age at any rate. Gilbert smiled and decided to be reassuring.

'I did say that,'

As they made to leave the house, sparing half a glance at the circle on the floor when they passed the kitchen, Gilbert stopped Arthur at the door.

'Remember, other people can't see me, so you can't talk to me or act like I'm there at all,'

'Can't you make me invisible as well?'

'So you didn't listen to everything after all. Glamour needs Marks, and you'll die if I put one on you.'

'You never said anything about that,'

That might have been true, but Gilbert didn't allow room for argument, smirking as he stepped outside onto the street and shaking his head mockingly as Arthur shot a dirty look at him. Doing his best to avoid losing the mundane on their way to the Institute, Gilbert suddenly remembered he was supposed to be meeting Matthias, then figured it could wait. Grinning to himself as Arthur looked past the glamour to admire the building, Gilbert retrieved his key and let them in. The Institute was quiet as they walked in, Gilbert laughed when Arthur commented on this, telling him it this was usually the case when he wasn't present. Judging by the look he received, he hadn't been doubted.

He left Arthur at the head's study to find Matthias after explaining the situation, but not before promising to talk to him again. Arthur could do with a guide to the Shadow World, and it wasn't like Gilbert didn't like him either.

They would meet again time after time, very little of their encounters ever intentional, at least not by both parties, but that wasn't to say either of them ever minded it.

I hope you enjoyed reading!