Severus gave up sleeping that night. He threw back the covers and quickly pulled on his robes. When he was as tense as this, only one place could make him relax - the Astronomy tower.

Carefully Severus opened his door and glanced up and down the corridor. It was empty. He quickly closed his door behind him and walked rapidly towards the tower. All around him, Hogwarts was quiet. The only light was the moonlight; the only noise was his soft footsteps. Even the pictures were sleeping. No huge crowds of students, all talking and giggling and not doing their homework like they should be. No bustling teachers, complaining about their workload and low pay. No Peeves making mischief.

Perfect.

Severus reached the tower door and quickly climbed up the steps, taking them two or three at a time. Finally he reached the top of the staircase and flung open the trapdoor.

The fresh air was a shock after climbing up the musty staircase. Severus clambered up onto the tower floor, not bothering to close the trapdoor. The tower was perfectly round, with a high stone wall bordering its edges. Severus walked over and looked down at the three hundred foot drop below. Normally, of course, he preferred his dungeon, but sometimes he just needed the fresh air and the solitude. Especially after having a class with the Weasley twins. Or Potter, for that matter.

Severus closed his eyes lazily. It was good that Erin was in his own house - he doubted she would have had a proper education in any other. He wouldn't tell her who she was, yet. Dumbledore thought he should, but then, Erin was his daughter. He'd decide what was best for her. And besides, thought Severus with a quick grimace, how do you explain to a fifteen-year old girl that she isn't who she thinks she is? Especially to a fifteen-year old girl that make you remember Angelina every time you look at her.

A sudden sound disrupted the silence - Severus opened his eyes and jerked his head to right, towards the Dark Forest. He caught a glimpse of a dark figure, riding what looked like a horse, but he couldn't be sure. Severus frowned. A student, out at night? Not likely. It could have been a Death Eater. But even a Death Eater wouldn't stray near the Dark Forest when it was so dark. Probably a centaur.

A few minutes later, Severus once more descended into Hogwarts. He was just walking quietly past the Slytherin house when the sound of voices floated through the thick wall. Some of the students were still awake.

Curious, Severus considered opening the door, but decided against it. Instead, he turned around and strode quickly to his office. Deactivating the protection spell, he walked in and put his hand on the left wall. Six stone blocks up and three to the left, he found what he was looking for.

One quick push, and the secret passageway was revealed. Severus doubled over and entered it. It took only a few seconds to reach the end, at which there was a massive, shimmering, mirror-like object. A one-way magic window to the Slytherin common room. Very useful for finding out what mischief his students were up to.

Severus crouched down even further and examined the window. There were four students sitting in the common room. They were arranged in a half-circle around the fire, so he could only see two of them. Blaise Zabini and Calvin Topin.

Blaise was speaking. "We can speak to Dumbledore, if you like."

A student in one of the chairs facing away from the window answered. "No, thank you," said Erin in a small voice.

Erin? thought Severus incredulously. What is she doing up so late?

"Blimey, Erin, you're in for a long haul," said Calvin, leaning forward. "You know Malfoy's going to make it hard on you, for being a -er - non-Pureblood. Not to mention the whole rest of Slytherin."

"Then why are you still here?" asked Erin, a slight challenge to her voice.

Calvin shrugged. "I figure there's got to be the exception that makes the rule. Truth tell, I'm half-and-half. I don't take the pedigree thing quite as seriously as some do."

"Sara?" Erin asked.

The fourth student spoke up. "I dunno. If the Sorting Hat put you in Slytherin, then you're a Slytherin and that's that."

"Blaise?"

Blaise thought for a moment. "You have to understand, Erin," she said slowly. "We're not exactly Slytherin's elite, either. Calvin's half- and-half. I've had no tolerance for Malfoy or his friends since first year, which is bad position to be in, considering Malfoy's social status. And Sara is simply seen as the happy-go-lucky glitter girl."

"Glitter girl?" asked Erin, sounding confused.

"Pretty airhead," translated Calvin. "What Blaise is trying to say is, you don't exactly have anything to gain from being friends with us."

"You might be better off convincing some of the others that you were just joking about your parents," said Sara.

"Lie?" asked Erin bitterly. "Why should I do that? You're right, Sara. The Sorting Hat put me here, and here I'll stay. As myself. If I have to fight my way through the ranks, so be it." Erin got up and paced - from the window, Severus could see that her pretty face had grown hard. Her voice had suddenly turned high and cold. "And I'll be kissed by a dementor before I suck up to that stupid prat Malfoy," she finished with a hiss.

"Watch it, Erin," warned Sara. "Remember, to Malfoy, you're just a stinky Mudblood."

If they only knew, thought Severus, turning around and going back to his office. If they only knew.