Pairings: Magnus/OC, Jace/Clary, Isabel/Simon implied, mention of Alec/Magnus and Magnus/Camille in the past (later)

Disclaimer: I don't own either of these amazing series. Cassandra Clare gets that privilege. Lucky duck! Though, I don't trust the ducks. :3

A/N: HI! So, I've been wanting to write an Infernal Device/Mortal Instruments Cross-over forever, but I couldn't come up with a story that inspired me! Then I offered to write a fic for my friend for Christmas and this was born! Here you are symmetricalravenxx8, I hope you enjoy it, honey!

"Just a bit longer," Magnus whispered mischievously causing the hairs at the base of Grace Lombard's neck to stir and sending a shiver down her spine.

She squirmed impatiently and whined to him in her posh British accent, "But, Magnus, you've been leading me around with this blindfold on for hours, love."

He rolled his eyes at her. While he had insisted that she be blindfolded for the past 30 minutes, it wasn't his fault! She wouldn't leave the apartment even to give him time to set up her birthday party- perhaps it was her aversion to parties thrown for her that led to her being so stubborn, but then again she was stubborn about most things. It was just part of her personality. You see, Grace Lombard was a warlock. She had been alive for centuries now, so many so that she usually couldn't recall her own age. The only thing she could tell you definitively about her age was that she was younger than Magnus. The younger warlock had known him for most of her life seeing as they had been best friends basically since meeting; and because of him, recently she had been introduced to the Shadowhunters of New York on her latest visit with him. With her eccentric yet completely lovable personality, she had fallen in with the Nephilim immediately. She even got along particularly well with Alec Lightwood, Magnus' ex-boyfriend, who had given her his blessing to date Magnus. She remembered the conversation well and with a smile she thought back a few weeks to when it had occurred.

~Flashback~

"Alec, can I tell you something?" Grace asked hesitantly. She knew that this would be a delicate subject with Alec as he still cared for Magnus, but she was unsure whether or not he still loved him.

"Of course," he replied with a smile and an encouraging nod. Alec had just met Grace a few weeks ago and already they were extremely close; he would even say they were nearing best friends- she was just that kind of person who you could become friends with in an instant and they were both extremely comfortable around each other- so he was curious about her hesitancy.

"Well, Magnus asked me to go on a date with him today, and I've no clue what to say to him!" she exclaimed nervously twirling some of her light brown hair between her fingers.

"I don't see why not," he said mildly. Despite Grace's doubts, Alec had fully bounced back from the break-up and wanted nothing more than for his new friend to be happy. "I mean unless you don't feel the same way about him," he said realization coloring his tone. He almost felt bad for Magnus now because Grace really was a very special girl and he could see why any man would want to be with her.

"I'm just not sure how I feel," she worried anxiously. "And I don't want to give him the wrong idea or lead him on! Magnus is one of my best friends- always has been."

"Well, whatever you decide, I want you to know that I am perfectly fine with it. Magnus and I are water under the bridge, so feel free to do what your heart is telling you, regardless of your worries about me," Alec quipped grinning at Grace as he saw right through her to her deeper concerns. She smiled radiantly at him and pulled him into a quick sideways hug before flitting out of the room with a brief, "Thanks, Alec!" yelled over her shoulder.

~End Flashback~

Just as Grace surfaced from her memories, Magnus was taking the blindfold off of her eyes and yelling, "Surprise!" along with the Shadowhunters that had become very close friends of hers.

She rolled her eyes at them and said, "Well it isn't really a surprise if I've known about since you started planning it, now is it?" She smirked at them and Magnus shook his head in exasperation while wrapping his arms around her waist.

"Wanna open your presents or not?" Jace asked his ever-present smirk mirroring hers.

She shrugged in acquiescence and took a seat on a huge cushy armchair that Magnus must have conjured up along with the rest of the furniture in his usually empty loft. Said warlock plopped down next to her making her tilt sideways and practically fall across his lap.

"You did that on purpose!" Grace exclaimed trying and failing to sound angry. Magnus simply chuckled at her as sat her back up, leaving his arms around her shoulders.

"Open mine first," he purred quietly handing her an oddly shaped object covered in layers upon layers of wrapping paper. "It was something that I got in London in- jeez, it was a lifetime ago."

She nodded, completely understanding what he meant, but didn't open the present. She just studied it closely, eyeing it suspiciously. "How much wrapping paper did you use on this thing?! You know they have these things called gift bags for all your oddly shaped gift-giving needs," she said laughing at her boyfriend as he frowned at her and pretended to be offended. "It's a good thing I have these then," she teased, letting her claws slide out. They were her mark- instead of cat eyes like Magnus, Ragnor Fell's whole exterior, or claws like the Dark Sister, Mrs. Black- she had retractable claws like a cat. She then drew her index finger along what she discerned was the bottom of the present, effectively slitting the paper all the way to the mysterious object. She then eagerly ripped the rest of the paper off, not bothering to put away the claws.

Once she had unwrapped it, Grace turned her head to the side to closely scrutinize the device in her hands, looking very much like a cat in the process. "What is it?" she inquired perplexedly.

Magnus gave a low laugh at her confusion and proceeded to clarify what exactly the strange thing was. "Since I know you do so enjoy the inventions of mortals almost as much as you love music- I said almost!" he exclaimed when she gave him the evil eye for even daring to compare anything to music. "Anyway, since you like that stuff I decided to find something old that maybe you could find some use for or, I don't know, just figure out. This was a component of an invention of Henry's that he never worked out how to get functioning. It was something he started later in life, so he passed before he could see it to completion." The Shadowhunters looked confused, but Grace had been told many times about the Nephilim of the London Institute that Magnus had grown so attached to in the late 19th century.

She started studying the device anew and asked a bit absently, "Do you know what he intended for it to be?"

"I don't know," Magnus admitted with a shrug. He was just glad that Grace liked the present!

"Hmmm, I wonder what this does," she muttered contemplatively, pressing a button on the side of the object after doing some rewiring.

Seemingly out of nowhere, a portal started to expand from the thing dragging all of the occupants of the room into the swirling darkness. Grace, Magnus, Alec, Clary, Jace, and Isabelle were sucked in, taking them God only knows where!

After what felt like an eternity, they all found themselves sprawled out in a cramped courtyard in front of a huge, castle-like church with towering spires and a wrought-iron gate surrounding the place. Grace rolled over and groaned. While the journey through the portal hadn't hurt per se, it did leave one aching and utterly exhausted, and the exhaustion was certainly weighing down on her. She was alternating between feeling like her bones had melted and were sloshing around in her bloodstream and feeling like they had turned to iron and were dragging her down into the Earth. Wearily she got up and checked on everyone else; as far as she could tell they were all fine but unconscious. When she got to Magnus he woke with a start and sat up quickly, only to hang his head and squeeze his eyes shut.

"What? What is it? What's wrong?" she asked anxiously hovering over him protectively.

"Nothing. Just- agh- headache," he ground out sounding pained.

"Is there anything I can do?" she asked softly bringing her hand up to the side of his face to stroke his cheek gently and smooth out the crease that had formed between his eyebrows.

"No- ah- I don't think so," he mumbled.

"Oh!" Magnus exclaimed suddenly. "It passed," he said smiling up at Grace's concerned face. Before she could pull away and stand back up he pulled her down and kissed her lightly on the lips and then pulled away, smirking at her dazed look.

She shook her head to clear away the cobwebs in her brain and then said, "Where do you think we are?"

Magnus took a real look around for the first time and his eyes went wide when he realized where and more importantly when they were. "No," he muttered inaudibly, then more clearly, "No we- we can't be. It's not possible!"

"What, dear?" Grace asked looking around perhaps for threats or some kind of impending danger.

"Gracie, we're- well, we're in London," he breathed out, shock clearly etched across his tanned face. At that moment three people tumbled out of the front doors of the building; they were laughing and conversing with each other and had yet to notice the six people scattered in the courtyard. "1878 from the looks of it," Magnus finished as a beautiful boy with dark black hair and piercing eyes the color of the night sky when it still holds remnants of blue- right before the pitch black darkness consumes all else. He stopped dead in his tracks and his companions looked at him oddly before noticing what had made their friend go still.

"Magnus?" the boy questioned, obviously bewildered.

You know how there's a box below these words where you can type your own words in? I highly suggest doing that. Maybe you can talk about my OC, the story, if you think I should continue, your opinion, or you know what you had for breakfast or something :3

Seriously, though, I don't know if this warrants continuing, so tell me if you want to read more. I'm going to mark it in-progress for now...