A/N: I just really needed some Sizzy fluff after I finished reading City of Lost Souls. So here, enjoy. I would say this takes place between Lost Souls and Heavenly Fire, maybe a little AU.

Snow Day

The sky was dark grey, and snow fell thick and fast. It soaked Isabelle in minutes, which gave her reason to mutter curses under her breath as she walked. She was on her way to Simon's apartment, to see him. She missed him when he wasn't around, and craved his company. It wasn't something that she liked to admit, but it was the truth. She couldn't bring herself to stay away from him for even a day, if it was her choice. Occasionally he had things to do, things that kept him busy for a day or two, but Isabelle had him to herself most of the time.

By the time Isabelle reached the apartment, even the t-shirt she was wearing under her sweater and jacket was soaked. Her hair was damp and frizzy, and she suspected that some of her makeup had worn off on the walk over here. Overall, it was not the way she wanted to look when she greeted Simon. She wanted to look pretty and confident, not frumpy and irritable. There wasn't much she could do about it, though. If she went home to repair the damage, she'd just have to walk back over here and risk ruining her delicate exterior again. She could always ask Simon to come to the Institute, but she didn't really want him to. She preferred spending time where he lived, rather than where her family was.

With a sigh, Isabelle pushed the buzzer and headed up the stairs when the door clicked open. She was reluctant to let Simon see her this way, but he already knew she was there. It was too late to turn back now. When he pulled the door open to let her in, his smile quickly turned into a laugh. "What happened to you?" he asked, looking amused.

"I got caught in the snow," Isabelle snapped, glaring at him. "Are you just going to stand there laughing at me, or are you going to let me in before I freeze to death?"

Simon's smile faded, and he stepped back to let her into the apartment. She stomped through the doorway, feeling annoyed with herself for being short with Simon. It wasn't his fault that it had started snowing heavily on her way over here. She made a mental note to not let her temper get the better of her. She dropped the small handbag she and brought on the counter and turned to face Simon again. She asked, "Where's Jordan?"

"Out," Simon answered. "With Maia. We have the place to ourselves." His smile returned.

"I'm going to take a shower, then," Isabelle announced, peeling off her jacket and sweater. Her black t-shirt was plastered to her body, and she shivered as the air hit her bare arms. "If that's okay with you," she added, glancing at Simon.

"Sure," Simon said, shrugging. He headed over to the futon and dropped onto it. "I'll watch TV while I wait."

Isabelle threw her outwear on the counter over her bag, and pulled off her boots and wet socks. She headed into the bathroom, turned the shower on, and stripped the rest of her wet clothes off. Without the wet fabrics against her skin, she began to warm up. When she stepped into the shower, the hot water scalded her skin and washed away all traces of the icy snow. She reached down and grabbed a bottle of apple shampoo, which she assumed was Maia's. Neither of the boys seemed like they'd want to go around smelling like fruit. She wasn't particularly fond of the fake apple smell, but it was better than smelling like a boy.

When she was finished, Isabelle wrapped her wet hair in one towel and wrapped the rest of her body in a second. Her bra was still pretty wet, but her underwear was almost completely dry. She slipped them on under her towel and left the bathroom. Padding barefoot out into the living room, Isabelle leaned against the wall to see what Simon was watching. It looked like a documentary on some mundane war, something Isabelle didn't really care about. "Do you have some clothes I can borrow?"

Simon jumped on the futon, startled. He seemed to have been lost in thought, and hadn't been paying attention to the TV. Nor had he heard Isabelle emerge from her shower. "Yeah, sure," he said, getting up. He grabbed the remote and turned the television off, before leading the way to his room.

Bending over the small dresser he had recently added to the room, he pulled out a worn green t-shirt and what appeared to be a pair of basketball shorts. Isabelle could hardly believe he owned basketball shorts, until she noticed that they were exercise shorts from school. He tossed the clothes to Isabelle, and turned to leave. "You don't have to go," she blurted, hardly believe that she had said it. She hated it when she sounded like she needed someone, hated it even when she sounded like she wanted someone around. She could feel the heat rising in her cheeks, turning her pale skin a deep shade of pink.

"Okay," Simon said, sounding uncertain. His brown eyes were questioning, but Isabelle couldn't bring herself to meet his gaze.

"Turn around," she instructed.

Simon did as he was told. When his back was to her, she let her towel drop to the floor, and she pulled on the t-shirt and shorts he had lent her. They were surprisingly comfortable; the fabric of the shorts felt almost silky, and the faded shirt was soft and warm. She unwrapped the towel on her head, letting her hair fall, wet and tangled. Falling nearly to her waist, she knew it would quickly soak the back of her shirt. "I'll be right back," she said, grabbing her towel again.

In the kitchen, she took a small brush out of her bag and ran it through her hair. The silky locks parted easily, and when she had brushed all the tangles out, she did her best to squeeze the excess water from her hair. With her hair sufficiently dryer, she returned to Simon's room. He was sitting on the edge of his bed, waiting for her. He had his hands clasped in his lap, and he was looking down.

"Hi," she said.

He looked up. "Hey."

Isabelle hugged her arms. "It's kind of cold in here," she said, feeling a little awkward. She wasn't always sure how to act around Simon, or even what their relationship was. They kissed a lot, but neither of them had tried to label anything yet. Isabelle usually preferred it that way, but not this time.

Simon got to his feet, threw the covers back, and crawled into the corner, leaning back against the pillows. He held his arms out for Isabelle, who immediately crawled into bed beside him. He pulled the covers over them as Isabelle snuggled against him, pressing her face against his chest. She felt Simon's arms tighten around her and his lips press softly against her hair. "Izzy," he murmured.

She turned her face upward and kissed his neck. Normally she would have left a lipstick mark, but she hadn't reapplied any makeup after her shower. It wasn't like she could carry her makeup kit around with her all the time, so today was one of the rare occasions Simon got to see her without her carefully painted mask. It had been bothering her less lately, to be seen bare-skinned, even less so with Simon.

Simon drew her closer, if that was at all possible, and touched his lips gently to hers. The soft, tender touch lasted for hardly any time at all. It was quickly burned away by a fierce hunger, the desire to be close to him, to kiss him and run her hands over his cool skin. She felt flushed, as if her skin was on fire where Simon's hands brushed her. His tongue wrestled with hers, and she suddenly tasted blood. She wasn't sure whose blood it was, until Simon pulled away briefly, panting. She knew he didn't have to breathe anymore, but it must have been a natural reaction he couldn't control. "Maybe you should be the vampire," he teased, and Isabelle noticed that his lip was bleeding.

She wondered briefly if she should apologize, but she was more interested in getting back to kissing him. She yanked his shirt over his head, and pulled his mouth back down to hers, running her hands over his bare chest and back greedily. His skin was smooth and frigid under her fingers. He lacked the lifetime of scars that she was accustomed to, the scars of battle and faded runes that marked a Shadowhunter. Though to be fair, she had only dated a couple of Shadowhunters. Mostly she stuck to Downworlders.

"Isabelle," he said, sounding breathless.

"What?" Isabelle asked, still kissing him forcefully. She pushed Simon onto his back and pressed herself against him, but he pushed her away. His touch was gentle, his gaze filled with something that Isabelle couldn't describe. "What?" she repeated.

"Slow down," he said, reaching over to brush a lock of damp hair out of her face. "You do know what you're doing, right?"

"Oh Simon," Isabelle said, smiling. "Of course I know what I'm doing. I know exactly what I'm doing."

"I should go," Isabelle sighed, reaching for her phone. It was almost dinnertime, meaning she had been with Simon for seven hours. She didn't want to leave the comfort of his arms, or change out of his old t-shirt. She couldn't stop herself from running her fingers over it, again and again. It was so soft, reminding her of the fabric that was often used for baby clothes and sheets. She knew that this kind of feel only came when a shirt had been worn and washed many times, meaning this was one of Simon's favorites. The faded lettering on it read, I got out of bed for this? Ironic.

"Probably," Simon agreed, but she could hear it in his voice. He didn't want her to go any more than she wanted to leave. The idea pleased her immensely. She smiled, knowing he couldn't see her. Her head rested on his bare chest, but there was no warmth coming from him. She couldn't hear his heartbeat.

It didn't matter. Just being there beside him made her heart beat nearly twice as fast. She wondered if he could hear it. He probably could, since vampires had such good hearing. It was embarrassing to think that he knew what she was thinking and feeling just by the way her heart sounded. She sat up, her long hair brushing against his skin, and pushed the covers back. She stood up and stretched. "I'm going to go change."

"Alright," Simon answered, sounding absent-minded.

Isabelle gathered up her clothes, which were still strewn around the apartment, and headed into the bathroom to change. She noted that Jordan hadn't come home yet, and wondered where he and Maia had spent the day. She pulled Simon's shorts off, and put her jeans on. They were still slightly damp, but Isabelle would just change out of them again when she got home. She glanced down at the shirt then, Simon's shirt, and made a split-second decision. She quickly slipped her bra on underneath it, and pulled her sweater on over it, and put her jacket on over that. She grabbed her own t-shirt and stuffed it into her bag.

She put her socks and boots on, and brushed her hair out again. She didn't want anyone to suspect anything when she got home, though she didn't think her mother really cared all that much what she spent her day doing. Alec might, though. Or Jace. They were overly-protective of her sometimes, because she was their sister.

Returning to Simon's rom, she found him making his bed, his t-shirt back on. "I'm leaving," she said, leaning against the doorframe.

He came over to her, pulling her into a hug. They stood still, their arms around each other. It was nothing like what had happened a few hours before, but it made her heart turn a somersault. The advice that Clary had given her recently came back to her suddenly. She had been debating about it for days, but right now, in his arms, she knew Clary was right.

"Simon?"

"Hmm?"

She had never been good at giving speeches or sounding witty. She was nothing like Jace was when it came to words. Now was no exception, and everything just sort of spilled out of her mouth, with absolutely no eloquence to it. "I need you," she said. "In my life. All the time, every day. I want to be with you, and I hate when I'm away from you, and I just… I wanted to make sure you know that."

She wasn't sure what kind of response she had been expecting, but Isabelle could see shock written all over Simon's face. This confused her.

"Izzy," he said, in a sort of faraway voice. "I thought…"

"What?" Isabelle asked, uncertain. Was he going to turn her down? That had never happened to her before, and it couldn't be happening now! Not with Simon, not with the first boy she had ever truly cared about.

"If you want me to be honest," Simon began, "I thought this was just a game for you. A fling."

Silently, Isabelle shook her head.

"I wanted to stop seeing you," Simon admitted. "I wanted to stop this before you got bored with me and moved on. I couldn't do it, though. I think I'm in love with you, Isabelle."

"Like you were with Clary?" The words were out of her mouth before she could stop them, but she hadn't asked out of bitterness or resentment. She was merely curious.

"No," Simon said slowly. "This is… different. Much different. All I really know is, I want to be with you. All the time."

Isabelle couldn't stop the smile from spreading across her face. This was the moment she was supposed to play it cool, act like she didn't really care about what he was saying. But that was impossible, but she cared very much about what he was saying. He was saying all the right things, making her feel as though she would almost burst with the happiness that was inflating in her chest. She leaned towards him and kissed him, very lightly. It was a soft, lingering kiss.

"I have to go," she murmured, pulling away. "But I'll be back."

"I know," Simon said. There was no cockiness in the grin that was plastered across his face. She knew, from the look on his face and the light in his eyes, that he would be there for her, every day, all the time.

As she turned on her heel and headed down the hall and out the door, she couldn't help but think that this was the best snow day she had ever had.