Tom Riddle

Their conversations never lasted long; they were enough to get to know each other, or perhaps... also, enough for their gazes to end up meeting from opposite ends of the Great Hall. It seemed like a coincidence, but later, it stopped seeming like one. Every time you looked up, Tom was already watching you; and, curiously, when you looked first, he never hesitated to return the gaze; because although he never smiled, he never looked away first.
...
You didn't know that Tom knew your schedule better than you did yourself, and had even discovered your most casual habits. And above all, he didn't keep a written list because he didn't need one; he stored every detail with an almost sickly precision, not because he wanted to use that information, but because the idea of not knowing something about you was unbearable to him.
...
"For next week, you will research the properties of the oldest magical poisons in Europe and their known antidotes."
The professor's voice echoed through the Potions classroom. "You will work in pairs." Before you could react, Slughorn had already spoken.
"Riddle... you with..."
He pronounced your last name.
Tom barely tilted his head, somewhat indifferent, but inside he knew he had gotten what he wanted.
...
The library remained closed that afternoon.
Madam Pince was arguing with two professors while several books fluttered uncontrollably between the shelves. A group of students had accidentally opened a defensive magic volume with protection enchantments still active.
Dozens of books had begun launching pages like paper blades, and entire bookshelves remained under containment spells.
No one could enter.
"Until tomorrow!" Madam Pince repeated with irritation to the students who began to disperse.
You let out a small sigh. "I guess we'll have to do it another day..."
Tom shook his head slowly and rejected the idea. You looked at him.
"I have the books we need."
He paused briefly.
"In my room."