A ferret.

All the malicious jibes she'd ever directed against Malfoy after Fourth Year had come back to roost. Hermione stared at herself in the mirror she'd installed in her lab in anticipation of her first successful transformation into her Animagus form. The meditations, chanting, mandrake leaf, and brewing had all gone well. The month long process had been exhaustive but she had done it.

Well, technically a stoat not a ferret. Still a mustelid, though.

God, this was embarrassing.

Hermione twisted her head to inspect her lithe body and shortish bushy tail. Her coat was winter white, commonly called ermine, rather than the brown with white underbelly she would have during the warmer months. Assuming her fur changed with the season. Her coat might only lighten to the sandy blonde of her natural hair colour.

She had a ridiculously cute little pink nose. Hermione bared her teeth at her reflection, twitching the black tuft tip of her tail. It was just as well Cathal wasn't friends with Harry or Ron because she would never hear the end of this. She had assumed from her meditations that she would be an otter. One dreamy vision of a sleek tubular furry critter was much like another.

She shivered when she touched her whiskers to the cold glass of the mirror. Her face tingled with the nerve response. Smells! It was a shock to realise how poor the human sense of smell was now she could sniff properly. The lab was a cornucopia of odours with the scent of nettles almost overpowering. She needed to get some better ventilation.

Hermione investigated her domain, climbing inelegantly over everything, squirming into tight spaces and under cushions. She stuck her nose in one of her dehydrated food experiments wondering if she could use her bestial senses to refine the spells. What she got was a snoot full of desiccated potato, which itched and had her in paroxysms of sneezes that made her jump about as though doing the weasel war dance.

She sneezed herself right out of her stoat body ending sprawled on the floor dusty and disorientated. Hermione pushed up into a sitting position to wait out the dizziness and the strobing visual distortions as her brain processed the return of the colour red. The witch was immeasurably pleased with herself if rueful that her animal form was ideal for investigating the pipes and conduits of the castle.

Heading back to the Slytherin dorm for an early night, Hermione was thankful Malfoy was not in evidence. She didn't think she could hide her grimace at the pasty ferret boy. She put herself to bed deliberately not thinking about the Chamber of Secrets. Had to be done, no question, but the excursion would be better left for the Easter holidays.

That night she dreamed chaotically and woke sweating despite the sluggard spring not yet touching the dungeons. Rolling out of bed to shower hoping to rouse herself, Hermione swore when her feet touched the icy floor. There was plenty of hot water in the bathroom. She stuck herself under the spray. Today would be an outdoor day. The weather was still grey, the snow not yet melted. Bleak and miserable, but she needed to air out her head.

A Tempus Charm after she had dressed made her swear again. It was just past six o'clock. The sun wasn't up yet. Hermione considered returning to her bed before stubbornly packing for a trek, taking herself out of the dungeons to the Great Hall and thence out the front entrance. Her breath misted in the frigid morn. Shrugging on her randoseru, the witch ran down the steps, scrunching through the slushy snow.

There was no one to see her hike towards Hogsmeade. Hermione set herself a brisk pace to keep warm, striding with Cathal's long legs. She needed to get more exercise. Cathal was taller and broader. She could carry more muscle, something few witches or wizards bothered about. Magic consumed a lot of calories, particularly complex charms and transfigurations. It took quite a bit of over-indulgence to achieve a Slughorn-style paunch.

She needed to be strong. Had she known going into the hunt for the Horcruxes how flesh-eating, depleting, draining it would be she would've spent Sixth Year eating like Ron. Magic consumed.

Next year when she was a Prefect, if Hogwarts got its way, she would be busy. She needed to increase her training. Likely she would receive an invitation to rejoin the Slytherin Duelling Club, which would sharpen her skills significantly. This year she had not been asked. That was entirely due to Violet Tripe, who was now a Seventh Year and not the forgiving type. The baleful witch had kept her distance, sating herself with cutting Cathal out of the influential social cliques.

Hermione could have protested but honestly no one cared about the feelings of a Slytherin, least of all her own House. Their own bloodlines and the Hat self-selected for sociopathic tendencies. Empathy was never going to abound in a group where Occlumency was seen as essential. Closing oneself off from emotions and emotional attachments was habit-forming. Being numb was a relief.

She skirted a slumbering Hogsmeade towards the forested uplands to test a hypothesis. Once she was definitely out of sight of the village, Hermione shrunk her randoseru and stowed it in her pocket. She wasn't sure whether it would transform with her. Her clothes would if she took her time to integrate them. A rushed shift caused the Animagus to shed their belongings. A fast escape with an awkward explanation on the return to a naked human.

With a moment of concentration, her body shrank down and down into her stoat form. Hermione gave herself an examinatorial sniff. Her backpack had changed with her. She could sort of feel it as a weight on her hip. Something itchy that shouldn't really be there. With a clawed hindfoot, she scratched the area. Nothing changed and the randoseru didn't reappear. She could transform with luggage. It was irritating but doable.

Jumping through the snow like a spring-loaded toy, Hermione made her way up the slope. She trilled as she leaped, twisting and kicking up her heels. Amazing! Bounce, bounce, bounce, splat into the snow. Her lack of coordination in her new body didn't remind her of waking up as Cathal. This was easier. Her limbs were responsive. She could move. She could climb right up a stump then stand on her hind feet to survey the terrain in front of her.

She had binocular vision though the definition wasn't as good as in her human form. Movement, however. That she could notice quickly. Like the gorse bush over there stirring with something behind it. Hermione smelled wet dog and human male and was throwing herself backwards towards a tree as the Grim lunged out of the shrubbery.

He snapped at the stump but she was already scrabbling up onto a branch beyond his reach. She climbed much better than he did and when he tried to follow he fell off, landing in the snow with a bark that sounded very like 'bugger'. The big shaggy dog paced around the trunk yapping at her. The stoat scrambled clumsily further out of reach.

The Grim became a man, made a snowball and threw it at her. She dodged. He threw another one, which caught her on the back. Hermione hunkered down trying to present as low a profile as she could while cursing herself. She had forgotten Sirius had hidden out in a cave to be close to Harry during the Tournament. They'd visited him once to talk and bring food. She hadn't remembered!

Fourth Year had been so much about arguing with Harry, adjudicating between him and Ron, frankly nagging, and frantically trying to do her schoolwork in between crises that Sirius had slipped her mind when recalling what she had done that year. Harry had exchanged letters with him and that was as far as she had bothered. Hermione hissed as she swore. Unbelievably thick!

Now she had to do something. She could either stay here waiting out the wizard getting bored, make a run for it, or reveal herself as human. Hermione edged through the tree, creeping towards the trunk as snowballs sporadically hit the branches. She gritted her teeth.

Sirius wasn't reliable. He went off half-cocked and he told Harry everything. If he found out Cathal was an Animagus then his godson would know within hours. And the more she talked to him, the more she would be tempted to try to save him. Hermione knew her own weaknesses. She hated, hated down her to core, that she had to let him die to preserve the timeline. If she changed form and they got chatting, she would let something slip.

She ran.

The ermine jumped and clawed and clambered from tree to tree, concerned only with putting as much distance between herself and the Animagus as quickly as possible. Sirius Black grew bored of pursuit and turned back to his cave. She kept going until she ran out of trees, tumbling off a pine branch in a cascade of snow before half-buried changing into her human form to run full pelt into Hogsmeade.

Hermione ducked under the eaves of Madam Puddifoot's, cast a Disillusionment Charm then smacked herself on the forehead. She had been distracted, over-focussed on the Animagus ritual, but she couldn't, absolutely could not afford to forget. Details had already been changed, she knew, and simply by her presence the future was skewed. But not too much, if she were careful. She needed to keep her wits about her.

As her heart-rate slowed and adrenaline ebbed, Hermione rationalised the encounter. Sirius had met Cathal before. He probably hadn't paid much mind to her last year as finding Pettigrew would have been far more important. It probably wasn't a disaster that she had chanced across him. She had been surprised and dismayed at that surprise. He might not have even realised she was an Animagus. There was no need to panic.

What she did need was a hot drink and a rest. Hermione took a deep breath then slowly exhaled. The strain was starting to show, she had to admit. Best to head back closer to the Hogwarts grounds. Maybe a walk around the lake would calm her. She didn't have classes today so she could have a nap in the afternoon. A day of doing nothing very much. Calmly. That was the ticket. She'd find some fucking serenity and not freak out over a small mistake.

She took a walk around the lake, in human then in stoat. Maybe it was the animal's instincts that had made her jumpy. Any sensible critter would run on seeing a huge dog leaping towards them. She'd treed herself without thinking. Hermione mused on this as she poked around the frozen edges of Black Lake. Her nose scented the fading winter, the fish coy beneath the ice, the lichen between the stones while her brain ran mazes.

If there was instinctual bleed-over between forms under stressful conditions, which she rather thought there was, then she would have to be careful in the pipes. It would be easy to become alarmed, do something animal and panicky then get herself into trouble. Into more trouble than sneaking into the Chamber of Secrets alone aged fourteen.

Moppet would go with her if she asked. Hermione was reluctant to test how forbidding Slytherin's wards were. Old magic settled into idiosyncratic grooves and ruts. They might be able to weasel, ha ha, their way through but if they got stuck she wasn't confidant of her ability to get them unstuck. She wasn't a Curse-Breaker.

They needed a means of communicating. A two-way mirror would be useful. A headset radio would be better as it left her hands free. A Protean Charm with audio rather than text might do. There was also the difficulty in hiding such a device. She'd chosen coins because they were plausible pocket debris. Matching jewellery would be noticed.

Hermione changed into human to do another circuit of the lake. The sun was well up now though most of the students would still be snuggled in bed. Early Saturday morning in March in Scotland was not alluring. How did you wear something or carry something without in being noticed or removed? It had to be a physical object, she wasn't going to touch magical tattoos, though it didn't have to be large or complex.

"Rosier!" The petulant voice intruded. She turned to see Malfoy striding through the slush unencumbered by Crabbe or Goyle. He was wearing his silly fur hat that was probably very expensive. Ron had said it made him look like a ponce. She had to agree. "I want a word with you."

"No." Hermione said placidly once he was within conversational range. "That's a good word."

"You can't avoid me forever." He huffed, cheeks pink from his rush to intercept her. He looked rather cute in a china doll sort of way; painted finely and coolly. "We need to talk."

"I haven't been avoiding you." She said, being contrary for the hell of it. "I simply don't care for your company."

"Rosier." Malfoy gritted his teeth. Hermione smiled at him and his clenched fists. "This is important."

"To you or to me?" Hermione asked, interested but not expecting much.

"To us." He ground the words out. She sighed. Continuing to be difficult about the conversation was unlikely to get him to bugger off if he hadn't stormed away already. Young Malfoy ran easily. It wasn't until Sixth Year when he stuck to something. To the great detriment of the school.

"I'm listening." She conceded.

"Father finally got your grandfather's papers." Getting into Rosier Hall had been arduous but that was apparently nothing to breaching the old man's study. Draco didn't know the details, which he resented. He wasn't a child! "Mother told me there's a betrothal contact between you and me."

"So?" Hermione made a mental note to contact Gringotts for confirmation of any documents lodged. The goblins couldn't tell her much until she was of age but Harnak probably would give her the nod if the Malfoys were trying anything.

"You can't shrug off a binding concord." Malfoy spoke sharply. Rosier seemed intent on ghosting through her obligations as though she wasn't webbed like the rest of them. "Father has lodged the contract with the Ministry. It'll be found to be legal." He was sure of that. His father's influence would make certain. "Mother thinks the match suitable."

"Again, so?" She took a breath. If he was actually trying to talk rather than dictate terms, she should at least try to parley. "We're not of age."

"Don't pretend to be obtuse. As the Head of the family, my father can marry me to whomever he likes. I'm not going to risk being disowned. As your guardian, Mother can endorse the contract." He paused to watch her expression. Rosier was good. Her face was mostly blank all the time. Someone might mistake her for being as thick as Goyle if she wasn't so precise in her retaliation when riled. "All she needs is your consent, and believe me, she'll get it."

"No, she won't." Hermione was adamant.

"Don't brush this off!" Malfoy snapped then flinched back when she leaned towards him. Her breath on his ear when she whispered sent lightning down his spine. His hair prickled, standing on end in what he hoped was arousal not fear.

"Not even under Crucio." She said implacably. "Trust me."

He didn't but he was convinced and left quickly, absolutely not asking why she sounded so completely certain. His father was strict with discipline, though he had never used an Unforgivable on his heir. Mother wouldn't have allowed it despite her own parents being very traditional in their control of their children. Rosier's mother was missing. That detail sparked in his mind. He didn't think it unrelated to her certainty.

The Muggle expression 'wearing a wire' had given her the idea. Magical objects didn't need to be functional. A pen could literally be mightier than a sword. All that mattered was whether the substance of the object could sustain the charms on it. You could enchant anything but the spells only lasted for as long as the physicality of the thing could sustain the energy. Paper decayed rapidly, diamonds were forever.

She chose gold because one of the pieces of Cathal's mother's jewellery Moppet had saved from the fire was a gold necklace. The circular chain links had melted and fused, which suited her purposes well. The metal was ductile enough for her to make wire without transfiguring it. Hermione wanted to limit the magical manipulation so the object was more resistant to a counter-spell.

The Worshipful Company of Goldsmiths was unlikely to offer her an endorsement for her work. She did her best to smooth and shape the metal before imbuing it with magic in a series of 'shells'. Someone would have to pick apart the spells within the matrix rather than hitting the wire with a Finite. There would probably be some disruption but the communication device wouldn't fail totally as the counter-spell would hit the shell first. In theory.

On one end, Hermione used the Twins' Extendible Ear Charm couched in a Muffliato, choking down the range of the first to millimetres and the radius of the second to three centimetres. On the other end went an Amplifying Charm. She then used a Protean charm at the maximum distance she could sustain a strong casting through Cathal. After that, she had a lie down. While pushing her spells was becoming easier, she could really understand now why Hogwarts had insisted on her needing time to master her magic in a new body.

She still had a headache on Monday, which made the clatter of repotting in Herbology especially painful. The Nifflers in Care of Magical Creatures kept trying to nibble on her hands and climb into her pockets. Before she left class, Professor Grubbly-Plank had to pat her down to make sure one of the little platypus creatures hadn't hitched a ride in her robes.

Double Divination hosted yet another dire prediction of doom for Harry Potter though this time from Ron throwing the bones. Hermione listened to him read his oculary tertia marvelling at how much he had got right. His Sibylline book was a ratty scroll that had obviously been squashed down the bottom of his bookbag. Parvati and Lavender had tuatara skin journals they wrote in with silver ink and kept wrapped in bullock hide to protect against 'influences'.

It was with a great sense of relief that Hermione immured herself in her lab. Moppet popped in a few minutes later excited to try their new communication device. The witch braided the gold wire into the house elf's hair just behind her right ear, anchoring it tightly with a double sheet bend so it wouldn't slip. Moppet did the same for Hermione. The metal was cold against their skin and a noticeable weight but not otherwise irritating.

They went to opposite sides of the room and whispered to the wall before returning to exchange messages. The pair repeated this process so Hermione could fine-tune the volume and clarity. Once the transmission was good, they separated to walk around Hogwarts for an hour trying not to look daft as they talked to themselves.

"Success, I think." Hermione observed when they were back in the laboratory. "Now let's see if the wire works in stoat form."

Moppet watched fascinated as her friend changed into a white furry snake with whiskers. The tube critter skittered off into the corner and made noise. Moppet didn't know what she said though she did hear the chitters.

"Can Miss understand Moppet?" The house elf asked from her corner of the lab. There was high pitched happy sound in response. They returned to their chairs and Hermione changed back.

"I can understand you." She combed her fingers through her hair, rumpled now from the morphing. "There's bound to be a spell for talking with animals. I'll try to find one that works for mustelids. I don't want to be stuck somewhere having to communicate with 'one squeak for no, two squeaks for yes'."

"Miss is putting off going into the pipes." Moppet observed.

"Yes." Hermione confirmed on a long sigh. "I am really not keen on this plan." She would do it though. However grotty, claustrophobic, or unsanitary the journey was, she needed to get into the Chamber of Secrets. "I'll go first day of the Easter Break, no quibbles. With luck, I'll be able to find a fairly dry pipe that leads directly there."

Fortuna did not smile on Hermione.

She found an entire book on animal speech charms in the Care of Magical Creatures section. There was a spell specifically for stoats and martens, which worked and meshed reasonably well with the other charms on Moppet's wire. They put their heads together so Hermione could listen to a plummy voice translate her vocalisations and laughed at the ye olde phrasing. However, it was intelligible so her last excuse was gone.

True to her promise, on the first night of the holidays Hermione was in the corridor outside Moaning Myrtle's bathroom. Her Map showed a rat's nest of pipes and conduits, intertwined like Medusa's hair. It stood to reason that the Basilisk would have used the most direct route available to it to respond to the Heir's call. Finding that route was the trick.

She scurried into the bathroom and used her claws to pry off the cover of a fairly clean smelling drain then wriggled her way into it. Hermione dropped down into a few centimetres of stagnant water and headed north. All the outflow pipes joined the large one the giant snake had evidently used, which was brick lined like a Victorian sewer with the addition of a narrow ledge on each side for the use of house elves when they did the mucking out.

According to Moppet, before a nineteenth century upgrade the plumbing of Hogwarts had been a hodgepodge of cess drains and water conjuration charms serviced by sluices that were perpetually prone to blockage. Headmaster Walter Aragon, a wizard obsessed with cleanliness, had overseen a refurbishment of the effluvia of Hogwarts. It was by his command that the main pipes were lit with safety lanterns to burn off the noxious gases, allowing Hermione to navigate by eerie bluish glow.

Down, around, in, out, and through she went following the large pipe. She didn't expect to get to the Chamber on her first foray. This was a surveying expedition to add definition to her Map. There were bound to be defences and wards in Slytherin's bolt-hole. If she were trapped, she wanted to be able to give Moppet clear directions as to where she was.

Hermione changed back into human at every major junction to chalk coordinate runes on the brickwork. In the fullness of time, clinging to obstinate optimism, she would be able to use this cartography process as part of her Runes Mistressship. She had an idea to expand the system to allow point-to-point Apparition through magical barriers and shields. Which she would be keeping to herself until the defeat of Tom Riddle.

When the pipe took a sudden sharp bend upwards before doubling over on itself, Hermione paused. Her fur prickled and there was a odour in the air that overcame the rankness. She sniffed, which was not something she particularly wanted to do, to get a better scent. Ozone and burned metal with an undertone of hot terracotta tile. Retreating to what she hoped was a safe distance, the witch became human again.

St Elmo's Fire danced from her fingertips.