Chapter 4: Swimming home

''What's wrong, sweetie?'' his mum asked as she lounged on the shore, thick fiery hair spread out across the sand, so very bright in the sun.

Harry was uncertain about how to express the onslaught of feelings as he looked up at the empty, empty castle looking out over the lake. It felt less friendly than it ought to be, to blame on its halls being empty of the presence that brought light to Harry's life. The season of blue skies and screeching birds seemed endless now he couldn't find it within himself to enjoy it as he had in the years prior.

''Why can't we show ourselves when the humans are here?'' he complained, resting his head on crossed arms as he longingly stared, dreaming already of the day his human would return. He imagined the small figure reading quietly while curled up against the cruel barrier separating them, fantasised about breaking it, reaching out to comb his fingers through hair that looked so much softer than his own.

Kind but stern, she lectured him: ''They possess powers that make it easy for them to harm us. The adults in the castle protect us, but there are hundreds of children playing with magic they don't quite understand or control yet. Surfacing outside of summer is far too dangerous for anyone but the Elders, who can cast protective magic of their own.''

''Sirius did it, and he's no Elder.'' Without waiting for an answer, he dragged himself a few inches further down the island to dunk his head and neck in the water and take a few gulps. Breathing air was coarse and unpleasant, the only thing of surface life he'd likely have a hard time getting used to. His parents had promised that his lungs would develop further with age, but Harry hadn't noticed much of a difference so far.

''Your Uncle took great risks,'' his mum retorts when he raises his head again, pressing her lips together. ''Risks that others paid a heavy price for. Poor Remus…'' she sighed, then looked away with sadness in her eyes as she fell silent.

''Remus?'' Harry asked, pushing himself up from the sand and sitting straighter. ''What do you mean?''

''An old story involving James, Sirius, and Remus' reckless adventures. You'd best ask them about it, as it's a rather touchy subject, but if you are yearning to meet humans, I believe it a lesson worth learning. In short, they are dangerous, be it with or without magic. Hundreds of humans who are barely starting out learning about their powers does not mingle well with keeping our own people out of harm's way.''

Harry vehemently disagreed. His human would never hurt him, their love wouldn't allow for it.

And so, Harry dreamt on.

Second year… after a depressing summer during which he'd longed more than anything to make the other children in the orphanage pay for every little thing they did to him or took from him – or in the case of the younger snotty brats for existing – and had to listen to the adults' hushed fears of a war brewing on the horizon, he was back at Hogwarts at last.

It hadn't been a dream. Not some drug-induced hallucination fed through syringes to keep him complacent. Hogwarts was real, standing strong as ever. There to welcome him home…

The only fear he'd had when exiting the train was the travel across the lake. For even if Harry didn't wish to hurt him, the curse wouldn't have broken by itself. What if other merpeople caught his scent? What if Harry would be overcome with madness or hunger and devour him before realising the tragedy that had befallen them?

Luckily, none of those fears turned out to be warranted as only the new students were ushered towards the lake, everyone else transported to the castle by carriages that appeared to pull themselves.

The lake still on his mind, Tom only paid enough attention to the feast to combat the gnawing hunger in his belly, stemming from two awful months of having been given scraps and needing to steal from every place in reach to get more, be it the orphanage's pantry, shops, or the hands of babes. It had felt dirty, Muggle, to be reduced to digging in the dirt. Maybe he should succumb to the Black lake, if only to wash the grime off…. Floating weightlessly to cushion the weight of his sins felt like the closest to salvation he'd ever come.

His thoughts were dragged towards the merfolk as if caught in a maelstrom, and Tom gravitated towards the window seat the moment he set foot in the Slytherin common room. It was unlikely for Harry to appear today, with it being a Monday. There was nonetheless a spark of hope, for Harry had visited during the very first day Tom had arrived at Hogwarts too. As long as there was a chance, he wouldn't want to miss it, not when Harry had come to embody a large part of the magic in Hogwarts in Tom's eyes.

Thus, he sat and waited.

Making himself comfortable, Tom put only the necessary minimal effort into performing social niceties when approached by other students. It was bothersome, but he'd made a reputation last year as Hogwarts' brightest new pupil, which meant others would vie for his attention now he wasn't an ickle firstie anymore. Walburga didn't approach but that was fine. She wanted to guide, not follow. If he were to get anywhere with his plans for Slytherin (which had become grander than ever, after a summer filled with sleepless nights from children crying and scratchy blankets had granted more than enough time to work out the details), he would need to start with those closest in reach. His dorm mates first, then perhaps some easily influenced first years, before trying to search for key figures to control in higher years – one of whom already owed him a favour.

As the hours ticked by, the common room emptied out as usual, hardly anyone able to resist the wonderfully soft fourposters awaiting them. Tom held out, getting a head start by reading the new schoolbooks for this year, which he'd had to hide from Mrs Cole well enough that he couldn't keep them in his room. Vaguely, he registered the clock striking midnight when he was engrossed in a riveting chapter on disarming charms. Less vague was the knock right next to his ear at the last chime.

Whirling around, Tom's gaze raked over the familiar, graceful form of the only friend he'd truly looked forward to seeing again: Harry, who'd given him the merfolk equivalent of bawling one's eyes out at the thought of their parting. Harry, who swam excited figure-eights in front of the window, now and then headbutting the glass as if he wanted to rub his head against Tom's leg. With a wide grin, the merman showed off a new treasure – a shiny pearl – and added it to the other baubles that were now strewn out across the ledge of stone in front of the window.

Harry, his very own companion. Someone Tom didn't have to share with anyone else.

And the world was suddenly right again.

Life was good. Fantastic, actually. Not perfect yet, with the barrier firmly in place, as pitiless of his pining as ever, but being able to see his human during the nights that Harry was allowed to join the hunts came pretty close. It'd taken a lot of begging to participate on the very night the green light appeared, as he'd already hunted the previous one, but Harry had managed to play upon the fact that he was a year older now and still untalented at anything else than catching fish. Whether Remus suspected foul play or not hardly mattered, as the man had caved without further questions asked.

So, the restlessness at last settled and routine returned, Harry's scheme continuing to work well. Moreover, he was so desperate to stay in the regular hunting parties that he didn't dare show up with bad hauls during the mornings now either even when holding some back on the days before his extra shifts. This resulted in quite some over-achieving, which all but Snape praised Harry for. His reflexes were so quick and his senses so attuned to sensing danger that could keep him from reaching the castle, that grabbing anything in reach on the trips back to the village became as natural as swimming.

''Can you swim?'' Harry asked one day as it occurred to him that if he couldn't move far on land, humans maybe couldn't move well in water.

The other stilled at the question, then slowly shook her pretty head.

That put a bit of a damper on Harry's visions for the future in which they could twirl around in the lake and he could show all of his favourite places. It also meant that their only possible first meeting spot would be on the shore, which was less than ideal due to it being, well, forbidden. That fact itself wasn't enough to stop Harry, but it did mean a better plan was a must, one he'd need to think upon long and hard so their chance wouldn't be ruined before the meeting happened.

For the time being, it was fine to see each other like this, where he could watch colourful spells and their effects, and look over his darling's shoulder at illustrations that were scattered across the pages between illegible script. Harry's favourite moments were those in which his human nodded off to the sound of singing. His voice had never been appreciated before, Flitwick breaking the news early on that Harry was a hopeless case who would never be able to understand subtlety of tone or the importance of certain lilts and trills. His girlfriend didn't care about any of that, eyes drooping in clear enjoyment whenever Harry gave a small performance.

The brightest day of all was when hands moved for the first time into a blooming flower in front of the throat:

'Sing'.

He'd been asked to sing.

Harry gave it is his all, the best performance of his lifetime.

The restricted section brought answers during the Christmas holidays. They weren't answers Tom liked, resulting in an incident which did not endear him to the librarian or to Malfoy, who'd accompanied him. Only false apologies and a claim of innocence besides otherwise 'completely accidental' magic enabled him to keep the permission slip Slughorn had granted days prior.

The short version of it was that Walburga had been painfully correct in her explanation of curse-breaking: Only the caster's death or a counter-curse would do the trick. Tom had interpreted that as having the option to pick a preferred method and vowing to counter it as he had no knowledge of who cast the curse in the first place. As it turned out, the explanation was to be taken literally. Each curse worked differently, so breaking it required one or the other. Some lingered after the caster was dead so long as the appropriate counter wasn't found. Others could not be circumvented by anything other than bloodshed of the one who'd placed it… which circled back to Tom having no clear path forward as 'doom curses' fell into that category.

Naturally, most culprits of such wrought magic went to great lengths to hide they'd been the one behind it in the first place. His only information to go on, based on the current Slytherin students all considering it some vague but known legend yet the teachers not getting involved and thus likely not believing in it, was a crude timeline. It must have been cast after the currently youngest Slytherin teacher (Professor Beery) had attended Hogwarts as a student, but before the current seventh-years had arrived for their first. Meaning he was looking at a timespan of roughly fifteen to thirty years ago.

''Are you unhappy? You look unhappy,'' Harry told him, a terrifically sad note to his voice.

Tom vaguely waved his hand, having no way to express the complicated thoughts that whirled through his mind about how he'd have to start an investigation and plan a murder of an unknown person who'd attended Hogwarts decades ago.

He wondered if the Merpeople knew. Not Harry, specifically, who clearly had no knowledge of the curse's existence, but there had to be older ones. For the legend to have spread enough rumours, something must have happened before, perhaps involving the caster and the one they'd attempted to doom with this. If so, Tom would need to relay this information to Harry, so the other could ask the rest of his kind.

The list of extracurricular skills, spells and activities Tom needed to devote attention to grew the longer he thought about it: Research methods of immortality, work his way into Pure-blood circles to gather information and lend himself credibility for an eventual overhaul of Slytherin House, learn dark magic to make others submit to his will more easily and inconspicuously kill people, and now, as a new point: learn mermish.

It took a few weeks until he'd checked with everyone in the castle to find a tutor for mermish. To his deep displeasure, the only person at Hogwarts fluent in the language turned out to be Albus Dumbledore, who acted as an interpreter during yearly meetings between Headmaster Dippet and the Merfolk leader.

Tom promptly replaced the bullet point with 'learn Legilimency', a topic he'd come across in the library. Learning post-graduate level mind magic in second year sounded far more doable than spending extra hours with his hated Transfiguration teacher.

It came to his attention some further weeks later that the resident expert in Legilimency was also Albus Dumbledore.

Stubborn to a fault, Tom decided to learn both subjects from books alone, if only to silently spite the condescending professor.

AN: regarding the timeline with 'war brewing': WWII started on September 1st 1939. However, Britain officially declared war on Germany on September 3rd, when Tom was already at Hogwarts. As such, for this year it would not have influenced his travel to Hogwarts.