A/N: I can't stop writing them! Feedback always much appreciated.

Disclaimer: Not mine. Quit reminding me.

Description: Minerva is fond of swimming in the lake, despite her feline side. She encounters something interesting.

Inspiration: Slytherin common room is below the lake, so it can have a skylight, right? Written after the release of Pottermore.

Dusk settled over the Hogwarts campus, dyeing the grounds and the lake varying shades of violets and fiery oranges. Minerva became just another part of the landscape, tinted the colors of the exceptionally beautiful sunset. She knew she could face serious repercussions if caught so late after curfew, despite being Head Girl, but it had been nearly three weeks and she found it difficult to wait for much longer. Her hand reached up to finger the gleaming badge pinned to her lapel unconsciously even as her other hand undid the clasp of her robes. As her crisp school uniform fell away from her, pooling in a fabric circle at her feet, she slipped into the lake, turning back once to cast a charm of concealment over her clothing after casting a bubble head charm for what felt like the thousandth time that year.

Her strokes were cautious at first as they always were, her tentative attempt to avoid detection from the castle windows; she never used magic to conceal herself when swimming. To do so would take away the little thrill she felt when there was a risk of being caught. The lake water's gentle lapping sounds eased her into as sense of calm, and as she neared the center of the lake her strokes became smooth and fluid, cupped hands neatly slicing through the murky green as her black hair fanned out behind her. Finally, as she neared the center of the lake, she slipped under the surface, slowly allowing her eyes to witness the green world beneath the swiftly darkening one above, different every time she saw it. She had nearly forgotten the wonderful feeling of water drifting against her skin, untempered by a prefect bathtub and untainted by perfumed soaps. It felt ironic that purifying agents tainted the water in her perception...

"Lumos," she whispered, drawing her wand out from its resting place. She swam still deeper, strange tendrils waving gently as she passed. She smiled to herself as she waved back comically. Still she continued on; she'd heard the rumors for the past seven years and wanted to see whether they had a basis in fact. The trouble however, would be finding the skylight…if skylight it could be called, under the lake, and if it existed.

Still she swam on, considering briefly with much amusement and little seriousness the idea of asking the Giant Squid for directions. Her loose hair was a hindrance now, waterlogged and containing some of the plant life in the lake. It dragged behind her, a black rippling sheet laced with green, contrasting starkly with the coral color of her swim suit. Her wand arm was extended, making careful sweeping motions so the light beam didn't waver, eyes always waiting for a telltale sign of enchanted glass.

The reflection was subtle and she would have missed it if the long tentacle hadn't gently turned her face in the direction of the glint of light on glass. She felt aghast at the contact and immediately entranced as she saw the skylight. Unbothered, the squid moved away through the water without so much as a backward glance, tentacles waving like cilia. Gryffindor bravery and catlike curiosity propelled Minerva to the glass panel- or it caused her limbs to do so. She ran her hands over the glass, frowning. If she was the first student-and she was quite certain she was-to see the skylight of the Slytherin common room from the lake, then it shouldn't have a distinctly used air about it. And yet…

She clung to the skylight like a polyp as she tried to pin down a rational explanation, unaware of how much she resembled a mermaid from Muggle children's picture books, so different from those that lived in the lake. It was in this state that he first saw her, planes of bare skin pale against the deep color of the lake, her hair a cloud of silky black strands interspersed with tangles of green from the kelp.

Tom's first thought was one he would chide himself for later. She looks nothing like the mermaids in the textbook, he had thought, and then, how childish. He dispassionately evaluated her features, trying to tie a name to the surreal picture he saw. He snapped as the name came to him: Minerva McGonagall, the Head Girl this year. He wouldn't have noticed, but being engrossed in his book, when she had cast a shadow across it he couldn't help but notice, initially peeved. The feeling intensified as the implications struck him: someone else potentially knew about the exit he had discovered; the shadow was far larger than the marine life and far smaller than the squid. And it didn't have a tail, so mermaids weren't a plausible option.

He had already returned to his reading, resolved to find out what else she knew of the school's secrets the next day. If she had discovered the skylight, a Slytherin secret, it was only a matter of time before she discovered it was an entrance, and as he well knew, one discovery led to another.

He hadn't expected the glass to crack.

He certainly hadn't expected the torrential downpour either.

After a quick silencing charm, Minerva was trying to figure out how to open the glass. And after several tries, her bubblehead charm close to exhaustion, one poorly-thought-out spell resulted in the glass cracking, and caving in promptly afterward.

As she fell through the hole into the quickly-flooding Slytherin common room, time seemed to slow for Tom. His hand was already at his pocket when the ceiling cracked; it had cast a spidery shadow on his book. Intuition told him the rest. One arm shielded his eyes as he peered at the source of water, while his wand arm cast a shield charm over McGonagall, protecting her from the falling shards from the meter-thick glass. She was already groping for her wand, standing by him once she found it.

"Why didn't it sound?" Tom asked, his voice sounding distant even as he yelled over the gushing water.

"Silencing charm," she called back. "I'll get help-"

"No," he said, eyes thoughtful rather than angry. "You've done quite enough.."

Minerva ignored him, turning to run to Dippet's office, glancing back at Tom, alone in the silent common room that was rapidly filling. What she saw made her stop.

With the finesse of a wizard decades his senior, Tom was wordlessly fusing the glass fragments back into the shape of the skylight hole, a look of intense concentration on his face. Murmuring incantations -and perhaps a few swear words- he levitated it. Beads of sweat mingled with the water on his face as he raised the glass panel. Minerva rushed over, her temporary paralysis ended, and aided him in returning the glass to its place.

"Fuse it," Tom spluttered into the water, shaking his head to expel it from his soaked hair. "Fuse it!" he repeated angrily when she only stared at him. "I can't hold this indefinitely you know!"

Bewildered, Minerva cast the spell, trying to do it quickly and effectively. Tom's face was paling from the exertion; she doubted he could continue levitating the glass much longer. As she finished, he staggered a step or two back, and rapidly sealed the new cracks that threatened a repeat of the incident. She retrieved his wand for him as it fell from his trembling hand, now raised to his face.

"You..." he managed. "You're cleaning the mess."

She dared to laugh. It sounded choked and timid, adding to her discomfort. Tom sank back into his armchair, a pale, long-fingered hand covering his face. He withdrew his hand and looked for his book, now a sodden, fragile mess. He stared at her wordlessly. Minerva wished he would become livid, infuriated, anything besides this displeased silence.

"I can try to fix it…." She faltered. If he could fix the glass, of course the book would be no trouble. "Of course if you'd rather I'd leave.." She trailed off again. Now it would seem as though she didn't want to take responsibility for the relative destruction she'd caused. Was there a trace of amusement in his eyes? She noticed the water had caused his lashes to stick together.

"I think-"

"I'll just-"

They had begun to speak simultaneously. Minerva blushed. "You go first." When the response she got was an arched eyebrow, she tried again. "Right then, I will. You were completely brilliant. I can hardly believe it and I saw it happen. I'll be sure to inform Professor Dippet when I turn myself in tomorrow. After I put the common room in order, of course." She paused, and saw he was still expectant. "And thank you for the shield charm. Being impaled with glass shards would a….unappealing way to go." Still Tom was silent. Awkwardly Minerva turned and set about drying the furniture and restoring the room to its previous appearance, hating that she hadn't been able to fix the situation herself. Why wouldn't he say anything? She suddenly was aware of her state of undress and her level of discomfort rose.

"Don't turn yourself in."

She ignored him, face heating as she efficiently finished her work. "Did you hear me?" She felt his hand on her shoulder, and she turned to face him.

"Why not? I'm Head Girl, it's not honest to pretend the scene never happened. And no one will know about the type of magic you're capable of! You deserve a reward, and I deserve detention." She pushed his hand from her shoulder.

"Your honesty is admirable," Tom said carefully. Too admirable."But no one was disturbed, and no one needs to know. Don't turn yourself in as a favor to me." He fell silent, knowing this was a demand she had no choice but to acquiesce to.

Minerva smiled wanly. "Why are you in Slytherin?" She cast a drying charm over his drenched clothes and then her own. "I owe you."

Wordlessly Tom took off his robe, handing it to her. "You can't go through the halls in…that."

Again her face heated. "I can't be seen in your robes either. Can you imagine the rumors if I were to leave this common room, in yourrobes?" She laughed. "I have a solution." She transformed, shrinking to a damp tabby, flattered by the obvious admiration in Tom's eyes.

"Cats don't swim," he said, smiling. She transformed back.

"This one does."

Tom knew she was nearly won over, and made a calculated move. He gently took her hand, and led her to the spot that served as the exit through the skylight. "Don't tell anyone," he murmured as they rose first through the glass and then through the lake water. "No one outside of Slytherin knows how to use the exit, and I don't intend to be known as the moron who showed a Gryffindor."

She had hastily grabbed at her clothes, pulling on the robe hurriedly. "I don't know how to-" she began, but he interrupted.

"Hogsmeade." Was he smiling? She couldn't tell in the moonlight, but it gave him a mysterious and impressive appearance. Had she known his intentions to bring her into his power-questing plans, she would have left him immediately, rather than start something she would later wish she never began.

"I'd love to." She stands there long after he leaves before returning to the castle, an inkblot on a masterpiece of a painting.

She doesn' t regret the swim not the discovery, nor even the events afterwards. She considers them worthy experiences. But she still regrets those three words of acceptance she gave him, and remembers his three to her.

At least he was wrong. Cats do swim. She was proof of that.