Isabelle saw it all unfold.

At least, that's how she likes to tell it. In fact, she practically half-orchestrated it, because that's just how nice she is. After all, she was the one who told Jace and Alec about the vacant apartment down her hallway.

Well, okay, she had thrown it out as a last resort when she heard they were looking for a new apartment, because who wants their brother and his best friend living just a few doors down from you? But as big brothers went (and Jace was practically her brother, having practically grown up with the Lightwood kids), they weren'tthat overbearing. Plus, they would probably have hot friends coming over all the time. A win-win situation, as she saw it.

"Just our luck the elevator broke down on moving day," Alec snorted, carrying a box and glancing over at her as they stomped up the stairs. "God, Izzy, how the hell are you doing this in heels? If you twist your ankle, it's your fault."

A sardonic voice trailed from behind her. "Also, do try to restrain yourself from falling into my arms, they're sort of occupied today, Isabelle. Although I wouldn't blame you."

She rolled her eyes. Okay, so her plan did have that one major flaw: she'd forgotten how annoying it was having those two around. "Oh, no, you've foiled my plan. And I was just practicing my swoon," she intoned flatly, balancing her cardboard box on her hip as Alec fumbled with the keys and Jace chuckled. She turned around to glare at the lanky blond figure nonchalantly leaning against the white plaster walls when a flash of coppery hair caught her attention.

It was the art student who lived across the hall from Alec and Jace's apartment, a petite redhead Isabelle had never talked to that was currently struggling with two grocery bags and a satchel as she came up the stairs.

Jace was by the girl's side in an instant. "Hey, you need some help there?"

"No, I've got it," the girl protested, trying to adjust her grip even as the strap of her bag began to slide down her thin shoulder.

"Oh, yeah, obviously." Tattooed arms immediately reached out and lifted a bag gently from her grasp. Izzy would have sworn he even lifted a hand to help her adjust her handbag, but the girl had turned to glare balefully up at him.

Jace smirked, shrugging a shoulder offhandedly. "I was being polite when I asked."

"I said I had it under control –" Her eyes widened when she noticed Alec and Isabelle. "Oh, you're the new guys."

"It would seem so," Jace smiled again. "So show me where to put this stuff, neighbor. It's much better than hauling up Alec's crap."

Alec turned around from having placed a box to prop the door open. "Hey, I'm not the one who has like, five crates of books waiting in the car –"

"Now, now, don't be jealous that I'm just fantastically educated and well-read –"

The girl let out a giggle, her vibrant hair rippling as she shook her head before turning to Isabelle. "Are they always like this?"

She snorted, eyeing her nails casually. "Yes. Trust me, I grew up with them. In fact, they can be much worse."

"Izzy's a liar, don't listen to her," Jace immediately cut in, watching as the redhead juggled a bag to her hip and fished in her purse for the flat keys.

She looked up at him through a curtain of hair. "Yeah, right. I'm Clarissa Morgenstern, by the way. Call me Clary."

He cocked his head slightly, a strange smile on his face. "Jace."

Isabelle's not quite sure how – maybe it had something to do with Clary attending the same university as the rest of them, and how convenient it was after or in-between classes to grab a drink at the coffeeshop and bakery next to the apartment – but somehow she learned to get used to having Clary's sketches left on a paper napkin at her Formica counter or visiting Clary for some milk to find Alec and Jace teaching her to play Halo on the PlayStation they dragged over from their apartment because she refused to leave the brownies in her oven. She even got used to Simon, Clary's best friend and constant companion (it didn't hurt things that he was actually pretty cute, in a scruffy way, even if he did wear weird t-shirts with phrases like "CHICK MAGNET" and "YESTERDAY WAS THE APOCALYPSE: TODAY WE HAVE A SERIOUS PROBLEM" emblazoned on them).

She first got a nagging idea of maybe one of the causes (or one of the side-effects, to this day, she's still not quite sure, nor does she really want to pry into it) on a sunny Friday afternoon.

"Hey, Clary, I brought you that nail polish you wanted," she smiled as Clary opened the door, wiggling the bottle of iridescent teal in her fingers.

"Thanks so much," Clary chirped, lighting up immediately and heading towards the couch, Isabelle not too far behind, maneuvering over the bump in the floorboards with practiced ease.

She stretched anxiously as Clary propped a foot up on the coffee table to paint her toes. "Ugh, I've got a date with Simon later tonight and I have no idea what to wear."

Clary didn't even bother looking up from her work, the tip of her tongue sticking out of the corner of her mouth in the way Isabelle knows it always does when she's concentrating. "Yeah, right. You always look great, Izzy, everyone knows that. Plus, it's not like Simon's exactly fashion-conscious." She glanced up and caught Isabelle's pout. "Oh, alright, you can check out my closet if you want. Most of it doesn't fit you, though."

"I could always wear one of your shorter dresses as a top," Isabelle pointed out, unruffled as she clipped along and throwing the closet door open. "Ooh, you've done a bit of shopping since I came here last. Some of this stuff's really cute – I can definitely see I've had an effect on you." She fingered swatches of silk and velvet reflectively, eyeing a cocktail dress the color of champagne and a blue babydoll blouse.

Noticing the dark shape of more clothes carelessly slung over the chair at the desk, Isabelle walked over only to have her fingers hit something distinctly tougher and thicker than cotton or polyester. She tugged only to have a huge leather jacket fall into her arms. A familiar, citrusy cologne wafted around her.

"Um, Clary? Is this what I think it is?"

"What?" Clary bellowed from the living room. "I can't hear you, Izzy."

Isabelle padded through the pocket-sized hallway, carrying the offending article of clothing. "Can you explain to me while you've got at least half of Jace's jackets and hoodies on your chair?"

"Shoot!" A swipe of turquoise trailed down the side of Clary's foot. She reached up and grabbed a Kleenex. "Um, well, it's really nothing, Izzy."

Isabelle perched resolutely on the edge of the coffee table. "Noooo, you're not getting away with that. Spill, Clary – are you blushing?"

The redhead was dabbing furiously at the excess nail polish, refusing to glance up. "No, I'm not. It's really nothing, it's just that well, Jace always notices when I'm cold, so he always gives me his jacket or hoodie. And I just keep forgetting to give it back to him. That's all."

Isabelle arched an eyebrow and let it be in favor of going back to finish up her outfit – that champagne cocktail dress would look great with her ruby necklace.

That night, though, as she and Simon walked back from their favorite diner (it hadn't been at all like the dates Isabelle went on – he'd been shy and awkward and very polite, and somehow, with his arm comfortably rested on her shoulders, she found she kind of liked it) she spotted a familiar trio winding their way through the park, probably coming home after Clary's shift at the club.

Alec was walking ahead and wrapping a plaid scarf around himself tightly, and Clary was trotting next to Jace, dressed in her typical work clothes: a tiny black skirt and a white blouse, hair pinned up in a sloppy bun. As Isabelle watched, Clary hugged herself tightly, rubbing her upper arms with her hands, shivering in the flimsy cotton. Jace, turning aside as he talked, immediately shrugged off his leather jacket without a murmur or even a sardonic eyebrow raise, draping it over Clary's shoulders though she glanced up to protest, probably noting how now he was only in a black long-sleeved tee. Jace, seemingly unbothered by this, merely scooped up the strands of red hair pinned under the jacket and laughed.

The more that one looks for something, the more one sees, Isabelle knows, and she couldn't stop now that she'd noticed. She noticed that Jace seldom teased her now, preferring to nag Clary, a wide grin on his face when the art student would finally whirl on him, cheeks flushed and big green eyes flashing. How whenever they visited the club and some drunk patron would grab Clary, a muscle in Jace's jaw jumped and his golden eyes narrowed, and how sometimes as they walked, Clary would look up at him, eyes scanning over his profile, and her fingers would clench the way they always did whenever she got the urge to draw whatever was before her, as if she was physically holding back the yearning to commit it to paper. Even better, the two of them were somehow oblivious to all of these, somehow ignoring Isabelle and Simon's mutterings about unbearable sexual tension.

The most dramatic development, however, she heard rather than saw. It was pretty late at night when she heard the footsteps coming out of the elevator (which had, after a load of complaints and bribing of the landlord using pastries, finally gotten repaired two months after Alec and Jace moved in).

"I can't believe you punched my brother!" Clary's outraged voice rang shrilly.

Jace sounded like he was stomping after her. "He hurt you, what was I supposed to do? Ignore the fact your brother just slapped you right in front of me? I know you're used to having grabby customers at the club, but there's a difference between Jonathan and say, Raphael Santiago."

She wasn't having it. "I had it under control. I dealt with him on a day-to-day basis before I moved here, believe it or not. I survived."

"Clary." The intimacy in the way he sighed her name sent shivers down Isabelle's spine.

"I'm not a child, Jace. I can take care of myself. I don't need you to protect me."

The pounding of boot against flimsy carpet flooring stopped. "I know that."

Clary sighed, a gust of air that whistled along the walls. "Then stop acting like it, like I'm weak or something – "

There was a light scoffing sound of incredulity. "You're the strongest person I know."

Silence suddenly descended upon the hallway.

Curious, Isabelle stepped up to peek through the peephole.

Jace had pinned Clary up against the wall as they kissed so fiercely she was almost afraid one of them would shatter into the other's arms.

He had braced one hand against the wall, the other cupping Clary's jaw, his thumb lingering on her cheekbone. As Isabelle watched, he lowered it to curl possessively into her hips as Clary slid hers up his shoulders to tug at the silky strands at the back of his neck, a smirk forming on rapidly swelling lips at the throaty groan this evoked from him, and Isabelle was way too sober to be seeing this, so she rapidly backed away and watched reruns of Teen Wolf to purge her mind.

Of course, that really didn't do anything, because as it turned out, Jace really had no sense of shame. The entire gang had been close to begin with, and now Jace and Clary were practically inseparable. Whenever they were together, one lazy and lightly tanned arm would always be around her shoulders or her waist, or busy plucking out hairpins from when they went out (which drove Isabelle absolutely crazy, seeing as she'd spent an hour and a half a bottle of hairspray on that). Plus, her apartment was apparently the best vantage point to witness good-morning kisses, goodnight kisses, I-missed-you kisses, you get the point.

"Goddamnit, Jace, if you don't stop making out with your girlfriend, she's going to get fired," Alec would mutter, annoyed, as they sat at the club. "I don't even care if you think that guy's ogling her."

"You've got a proper backroom somewhere, don't you? Go use it," Isabelle would snap. At least Clary had the decency to blush and stammer apologies, whereas Jace would simply smirk and whisper something probably not fit for child audiences in Clary's ear.

Isabelle, for her part, liked to retaliate by making out with Simon in front or Jace or Clary's apartment as much as possible (this left Alec in a black mood most days, though she often pointed out he wouldn't be such an obvious fifth wheel if he finally admitted his feelings for Clary's boss). She actually didn't mind all that much, despite her loudly repeated complaints. She'd never seen Jace so happy in his life – not to mention how Clary practically glowed these days.

Of course, she did mind whenever something disturbed her Saturday mornings. Saturday mornings were sacred, devoted to sleep and nothing else.

So she was understandably bothered when she heard a door slam at eight in the morning and the sound of heavy footsteps groggily trailing across the carpet.

"CLARY! WHERE'S MY HOODIE?"

A door creaked open slowly. "WHICH ONE?"

"MY FAVORITE ONE!"

"THEY'RE ALL 'YOUR FAVORITE ONE', THAT'S NOT SPECIFIC AT ALL!"

The third time this happened, Isabelle finally rolled out of bed, threw on her bathrobe, and flung open her door to growl at a boxer-clad Jace, "Maybe you wouldn't have this problem if you just,I don't know – moved in together?"

Tawny eyes blinked rapidly in surprise at her before she slammed the door shut.

A month later, they did.

So, their story began with moving, and that's how it ends. For the time being.

(Isabelle's pretty sure she'll eventually have to kick Jace into proposing, but she's content with the current state of affairs for now.)