Severus Snape would often sit in the library, pouring over thick books on various subjects. What he did not often do, however, was write. His hand flew across the parchment, his greasy hair obscuring most of his face. On the table he was sitting at lay a book, and Severus's eyes flicked back and forth from the book to his parchment. After several minutes, he turned the page, copying down anything he thought useful. The light from the closest library window had almost completely faded when a red-haired girl bounded towards him happily. She dragged a chair out from another table, still smiling.
"Mary said Flitwick is going to start us on Cheering Charms." She pronounced happily. "I've been looking forwards to it since the start of the year, it's supposed to be really good fun – what about you, Sev?"
The boy gave a non-committal grunt, his nose still an inch from the parchment.
"Sev?" She asked again, a small frown forming between her eyebrows. "Sev, are you even listening to me?"
"Hmm?" He finally looked up at the red-head, who rolled her eyes in annoyance. Severus continued to read through the book. The girl looked over curiously.
"Lycanthropy… Full Moon…" Her frown deepened and she eyed her friend. "What is this about?" This time the boy looked up, grinning.
"This" he announced, waving his hand at the bits of parchment and the old book "Is the fruit of my research. It's on werewolves." He leaned forwards, suddenly serious. It made him seem all the more strange. "Lily, I believe there is a werewolf at Hogwarts. Maybe two. I've been suspicious for a long time, and I think I know who it is. I think it's Remus Lupin."
Lily raised her eyebrows at him before bursting into giggles.
"You think," she said, doubled over, "You think, Remus Lupin is a werewolf?!" Lily was in hysterics now, drawing curious glances from several first years nearby.
"You don't believe me." Severus retorted mulishly. He crossed his arms, defiant. "Where do you think Lupin goes every month? On a full moon, too. He always comes back pale and tired looking. What about the scars on his face, then?"
Lily shook her head, finally able to control her humour.
"I'm going back to the common room. This is too funny." She chuckled, getting up and heading off. The ghostly sound of laughter echoed down the hall for the next minute, before finally fading away.
Severus sulked for a bit, tapping his quill against the table. Then, struck by an idea, he hurried to the window. The sun was almost down, a few golden streaks piercing the night sky. It couldn't be moonrise yet, could it? Severus stood at the glass for several minutes, his hooked nose stuck to it. Finally – there – three figures strode across the silvery lawn. Snape could just recognise one of the figures -it was definitely Madam Pomfrey- but the other two… One was quite tall, the other slightly shorter than Madam Pomfrey. They had walked almost out of sight by now, but they were coming to a halt on a hill… with a very familiar looking tree. Severus didn't see what happened next as they were too far away, but they never returned, not even when he watched for another 15 minutes.
That confirmed something, though. There were 2 werewolves in the school.