A/N: This is like, my longest one-shot ever! Woo! Okay, this is pre-Hesitation, but it's in the same little series, now called Definitions. So, hopefully you like it =D

Penetration is a moment of ecstasy for the attacker. The losing army penetrates their opponent's deepest defenses, and the battle is all but won by the underdog. A man penetrates a woman's barricades, and he has her heart forever.

One friend discovers another's secret, and the discovery penetrates the walls the latter has been building his entire life.

An uncommon silence filled the Gryffindor common room during Hogwarts' Christmas vacation. Every student but two had returned home for the holiday.

The first, having betrayed his pureblood, strictly Slytherin family by becoming a Gryffindor, was uninvited in his own home, and had been forced to stay behind at Hogwarts. This was Sirius Black.

The second was welcome to return home, but under a shroud of disapproval and disappointment. He chose to remain at Hogwarts because he would rather be alone than lonely. This was Remus Lupin.

At the moment, however, Sirius was alone in the common room, sitting in his favorite plush chair by the fireplace with his arms wrapped around his knees. He was frowning at the fireplace, wondering if his family even missed him, when the noise of feet coming down the stairs made him look up.

"Oh. I didn't realize anyone else was here," the intruder, Sirius' dorm mate Remus, apologized. "You don't mind if I sit here and read, do you?"

"No," answered Sirius, shaking his head. "I didn't realize anyone else was here either."

The first choose another armchair by the fire, assumed the same position as Sirius, and opened his book, which Sirius noticed was The Standard Book of Spells, Grade 1.

"Studying over break?" he asked, before he could help himself.

The boy looked up with a bit of a flush in his cheeks. "No, I just…I never thought I'd get to learn these spells, so now that I can…" He finished his sentence with a shrug and returned to the textbook.

Sirius' eyebrows furrowed. He didn't think he'd get to learn the spells…? What was that supposed to mean? The pureblood watched his roommate read. His eyes were moving so quickly they blurred, until he looked up and pointed his wand toward the fireplace.

"Incendio."

Instantly, a fire began, warm flames lapping at the logs. Sirius raised his eyebrows.

"That was cool."

A blush and a shy smile appeared on the boy's face. "Thanks."

Sirius wanted to say something more to the mysterious boy, but he couldn't think of anything to say. Instead, he tried to remember everything he'd learned about him.

He knew that he was fairly smart, and apt to perform any spell, as he had just demonstrated. He remembered that he barely spoke in any of his classes, except to say incantations and answer the occasional question. He remembered that he was sick fairly often, and, upon examining him again, Sirius noted that even then his cheeks were flushed and there were purple bags under his eyes.

"So why are you here over the holidays?" asked Sirius, uncomfortable in the silence.

"Oh. Well, my parents are in France for the holiday, so I thought it would be easier to just stay here."

A silence followed, in which Sirius realized Remus was lying, but decided not to call him out on it.

"And you?" asked Remus.

"My parents are angry I wasn't Sorted into Slytherin, so they didn't want me home," Sirius answered with a brave laugh. "I imagine I'll be spending all of my holidays here. It isn't so bad, though. The castle's weird when it's quiet, but I sort of like it."

Remus nodded, a little surprised that the boy he barely knew was so open about his family. He looked back down at the book, but found himself unable to focus, suspecting that the other boy was watching him. He shut the book and looked up.

Apparently, this was what Sirius was waiting for. "What's your favorite class, so far?" he asked, turning so that he faced Remus.

"Well, I like Transfiguration quite a bit, but I think I prefer Defense Against the Dark Arts," he answered.

"Me too," answered Sirius with a grin. "It's cool, you know, actually getting to learn about the real world and not just the perfect little world your parents hand you."

Remus didn't answer, but instead looked into the fire he had started. Sirius, sensing he had stuck a nerve somewhere, changed the subject.

"So do you think you'll try out for the Quidditch team next year?"

Remus shrugged noncommittally. "Probably not. I'm not a very good flyer. You are, though."

"Thanks," Sirius said, a faraway look in his eyes. "I think I'll go out for Beater. I prefer Seeking, but I wouldn't make it—you know James Potter? He's about a thousand times better than me. I'm a pretty good Beater, though. My brother and I play sometimes."

"You have a brother?" asked Remus.

"Oh, yeah, his name's Regulus," Sirius answered. "He's nine. I think he's more into my parents' idea of perfection than I am, so he'll probably end up in Slytherin."

Remus nodded and looked at the window. Startled to find that the sun was close to setting, he stood suddenly.

"We'd better get to dinner," he said, already starting toward the portrait hole.

"Good, I'm starving," Sirius said, standing and heading out of the hole behind his new friend.

Sirius talked as they made their way toward the Great Hall, speaking of everything from his favorite Quidditch team to what he hoped they would have to eat at dinner that night. He was surprised, then, to find that, by the time he reached the wooden doors leading into the Hall, Remus was gone. He spun around, wondering if he'd gotten stuck in a trick step, but there was no one on the stairs. In fact, there was no one in the entrance hall at all.

He frowned. He was sure the other boy had been behind him… He shrugged. He must have had to go back to the common room for something. He entered the Hall and sat in about the middle of the Gryffindor table. Not many had stayed from the other Houses, either; a group of Slytherins, three Hufflepuffs, and no Ravenclaws remained. Sirius sat and began to eat, waiting for Remus to show up.

But Remus never came. He sat and waited, but no one entered the Hall after him. Confused, he later entered the common room, expecting to find the boy there, but it was as empty as it had been before he entered.

Confused, Sirius considered going to Professor McGonagall and reporting that his dorm mate had disappeared, but he didn't want to look like a tattletale. The other boy was probably just off causing trouble, as Sirius himself had done a few times already. Suddenly quite tired, he headed up the stairs to the empty dormitory and fell asleep quite early.

When he awoke in the morning, it was still early. The sun was just barely coming up over the tops of the forest trees, and Sirius decided to sit in the window and watch the sunrise.

It was then that it occurred to him that Remus was still not back.

Now he was worried. Was he sick again? He hadn't looked good before dinner…and he apparently had never come to bed…

The full moon still shone in the distance, resisting the sun's reign over the sky. He stared at it until he could close his eyes and picture the exact way the moon looked.

And then, quite suddenly, it clicked.

With a bit of a gasp, Sirius looked again the moon, and then back at Remus' empty bed.

He felt a rush of pity for his friend. If he had chosen to stay at Hogwarts, it was only because he would face embarrassment or sympathy at home, and if he hadn't…

He let his thoughts wander for a while, until the door opened and shut, causing Sirius to jump.

Remus, looking exhausted and covered in scratches, entered the dorm, only to notice his roommate awake and staring at him.

"I—I—" he sputtered, trying to find an excuse.

"I know," Sirius answered, biting his lip.

Remus closed his eyes and shook his head. "No one was supposed to find out."

Despite the seriousness of the situation, Sirius smiled. "It was becoming sort of obvious."

Remus sat down on the end of his bunk. "You can't tell anyone. No one can know."

"I won't," Sirius promised, going to sit on the end of his own bunk. "It's not a big deal, anyway."

Remus' eyes widened. "Not a big deal? It's not a big deal that every month I transform into a hideous monster, prepared to kill anyone who gets in my way?"

Sirius frowned. "I think you need to relax. You didn't kill anyone, did you?"

"No," Remus answered reluctantly. "The shack in Hogsmeade? The one the villagers believe is haunted?"

"That's you?" asked Sirius, grinning again. "Cool."

Remus frowned, but didn't try to correct him. He was exhausted, and his eyes drooped.

"Your parents aren't in France, are they?" Sirius asked quietly.

"I'd rather be alone than lonely," answered Remus, looking away.

In that moment, Sirius penetrated the walls Remus had been building for years to keep others out. They both knew it. Remus realized he'd just made his first true friend at Hogwarts. Sirius smiled to himself as he stood.

"You should get some sleep," he suggested, gesturing to the bed.

"Yeah," Remus agreed, also standing before lying down on the bed.

"G'night, Moony," he said, returning to the window.

Remus frowned in contemplation as he pulled the covers over his body. "Moony?"

"Sure," said Sirius, grinning widely. "Full moon? Moony?"

"Oh," said Remus. "Okay. Good night."

A/N: Yay! Love it? Hate it? …review, please?