[AN]: I've had this story in my head for a while now, and it visits me whenever I listen to tracks 12 and 20 from the Half-Blood Prince soundtrack. I always thought it would be a one-shot, although I never really reached "the proper ending". So, updates may or may not ensue. I'm sorry.

October arrived with a biting chill in its air. Although it was still early in the term, Hogwarts students were already burdened with assignments. One sixth year student, Tom Marvolo Riddle, preferred to attend to his in private, as he always did with almost every other thing in his life. And, quite fittingly, the most secluded spot which he had decided on was in one north-east corner of the Black Lake, where the sunset looked most beautiful.

When he's finished with his assignments, Tom Riddle would stroll along the side of the Black Lake. It was autumn; all around him were dying leaves the colour of riot, of sunset itself. The walk had always been one way for him to relax and loosen the knots in his head, a habit.

Everything was going on ritually; the assignments, the tolling of bells from the high tower of the castle, the sunset. But there was something different in the ripples of the lake.

A splash drew Tom's attention to the body of water. It wasn't in its usual calm. He thought at first that he had imagined it, but he was immediately corrected; someone was indeed swimming in the cold water. In fact he had just reached the bit of grass where that someone had left their clothing.

He wondered for a moment if swimming in the lake was a punishable offense. Tom believed it ought to be, because no one should be allowed to go skinny dipping in the Black Lake in October. But it wasn't, and he had to leave the swimmer to their recklessness.

Be that as it may, he decided not to just leave it at that; because Tom Riddle was a Hogwarts prefect, and it was his duty to bother with people, especially when they were a Hogwarts student swimming in the Black Lake in October.

"Oi! Have you lost your mind?" he called out to his offender.

They seemed to have not heard him, or had otherwise chosen to ignore him. Either way, it seemed to Tom like a challenge. So he took out his wand and sent a jet of red light their way as a warning.

That gave Tom his intended result, and the swimmer began heading for the bank. Judging from the uniform lying on the grass before him, Tom assumed that it was a boy in the first year. But then it turned out that the first-year was a girl; she climbed out of the water completely naked, prompting him to blush furiously, turn away, and feel stupid for the first time in his life, which was an unnatural feeling for him and he didn't like it.

"Is it against the rules to swim in the Lake?" he heard her ask with surprising evenness.

"Are you decent?"

"What do you mean?"

"Just get dressed!"

Still with his back to her, Tom asked, "Is there anyone else with you?"

"No. Am I in trouble?" her tone was still flat.

"Well, it isn't against the rules, but apparently it should be; one would think even a first-year would have the sense not to go swimming at this time of year."

"Why so? You can look now."

Tom turned to face her. "What do you mean, 'why so'? The cold could've killed you!"

"But it isn't cold."

He blinked and began to suspect that the cold really had killed her after all. That is, only mentally. "Did you steal this uniform?" he asked, indicating the Ravenclaw badge on her robes.

"No. Why would you think that?"

"I didn't think Hogwarts would accept intakes from asylums."

"Oh. I guess I'm the exception."

Tom scorned at her for this. "Don't try to be smart with me."

"Can I go?" she requested, and Tom granted her leave. The girl headed back for the castle, dripping wet in her robes.

"Unbelievable." He disliked the girl already.

The next day, Tom went down to his corner of the Lake again, but only to start hating the girl from yesterday afternoon; there she was again, intruding upon his privacy by swimming in the lake. He crossed his arms and decided to wait.

The sun was setting when the girl finally got out of the water. Tom didn't bother to look away this time; it wasn't like there was anything to look at anyway.

He also didn't bother greeting her first. "You need to stop doing this."

"Doing what?"

Couldn't she at least have brought a towel with her? One can see right through her shirt!

"Are you sure the cold hadn't killed your senses? It must be freezing in the water!" In all truthfulness, Tom couldn't have cared less if she died in the water, but he had expectations to meet; he'll be damned if he let someone drown themselves when he was around to do something about it.

"Have you been in the water?" There was genuine curiosity in her voice.

"No."

"How can you tell it is freezing?"

"The air is cold!"

"They're not the same thing, are they?"

"Don't try to be smart with me!"

"What does that even mean?"

At that moment, finishing her off felt like the most righteous thing to do; his hand was already reaching for his wand. But Tom Riddle was more reasonable than that. This was just a little girl who asked a lot of questions, which is what little children do. Her tone had not so far been impolite, either. Tom sighed, rolling his eyes.

"Maybe you should try the water once. I promise it isn't cold. And I always keep my promises."

His eyes widened, if only a little. This kid cannot be serious. "Come on, back to the castle."

The next day was a Hogsmeade Saturday, and Tom Riddle was hoping to have the Lake all to himself again. But he was disappointed; the reckless child had apparently made a habit of going swimming in the afternoon.

She always keeps her promises, huh?

He approached the bank and pulled back his right sleeve. Then he dipped his arm up to the elbow into the water, and was surprised to find that it was a lot less cold than he had thought it would be. Still, it wasn't the right temperature for swimming. Tom withdrew his hand and turned his attention to the little girl; she hadn't gotten very far yet.

For reasons unfathomable, he began taking off his shoes and socks, and shed his outer robes, and then Tom went for the water. Near the bank, it reached up to his waist.

"It gets better towards the middle." Her sudden reappearance startled him. He gave her a questioning look.

"I meant the temperature."

"If you say so."

"Let's go visit the Giant Squid!" she suggested with a grin. She had fangs in her smile. And there was something ...odd about her general appearance.

Even though he already felt violated by the child's intrusion upon his private afternoon walks at the lake, Tom did not deny that the lake was expansive. "I don't think we can swim out that far."

At that, she dived back into the water.

"Hey!" Was he the one who's actually out of his mind, talking to children who swim in the Black Lake in October?

Her re-emergence from the water a moment later was unnerving; her stealth was deadly. She held out an open palm to him, on it was a certain type of water plant.

So that's what was off about her appearance. "Gillyweed," he identified it, and then proceeded to ingest it. Gradually, the water felt warmer and warmer to him, and the air suffocating. Then Tom dived into the water after the little girl.