Bagsy tapped out the rhythm to Helga Hufflepuff on the barrel before crouching her way into the Hufflepuff common room, Mezrielda close behind her. Soon they were standing, silent, in the middle of the room, surrounded by comfy armchairs, dancing cacti, ferns peacefully swaying from side to side, and oak desks piled high with different school books and quills.

'Well?' Mezrielda folded her arms expectantly. Bagsy was desperately trying to point at the round door hidden behind the armchair and the ferns, but it was as if she were a statue, unable to move. 'Bagsy?' Mezrielda pushed.

'I'm trying to show you where – I'm trying to point, but it's not – I don't understand what's going on…' Bagsy wondered if she'd been hit by some terrible curse.

'You didn't brew it in your dormitory?' Mezrielda asked. Bagsy nodded her head. 'And you didn't brew it out here?' Bagsy nodded her head again. 'But you did brew it somewhere in the Hufflepuff burrow?' Bagsy nodded. 'But not in anyone else's dormitories, either?' Bagsy nodded a final time. Mezrielda placed her hands on her hips and paced around the room. She poked bricks on the wall, peered out windows, peaked below sofas, and even, to Bagsy surprise, pulled the ferns back behind the armchair and stared directly at the round door, yet didn't seem to see it. Mezrielda came back to Bagsy. 'Did I go near where you brewed the potion?' she asked. Bagsy found she couldn't answer. 'Don't worry, Bagsy,' Mezrielda said confidently, the hint of a smirk gracing her lips. 'I think I've figured out the issue, here. I need you to do one more thing for me to be sure. Go into the place you brewed the potion, grab it as quickly as you can, and come back out.'

Bagsy nodded and, taking a deep breath of fresh air, ducked behind the armchair and through the hidden door.

'I knew it…' she heard Mezrielda hiss from behind her as she entered her private room. Almost instantly her skin began to prickle, and her throat recoiled at the stench of the potion. She grabbed the filled cauldron from her desk and hurried back out. At first Mezrielda's eyes seemed to slide past her until Bagsy took a few steps forward and they locked onto her face.

'Here,' Bagsy coughed, holding the cauldron out to Mezrielda who took it, looking curiously at Bagsy's paling hands. Mezrielda didn't seem to react to the potion's fumes at all.

'Evanesco,' Mezrielda cast, swirling her wand above the cauldron's contents which disappeared, as if melting into the air. She handed the cauldron back to Bagsy.

'Thank you,' Bagsy sighed in relief.

'Bagsy,' Mezrielda began, 'have you ever heard of the fidelius charm?' Bagsy shook her head. 'To over-simplify, a secret keeper is chosen who is given information, like the existence and location of a hidden room, and only the secret keeper, and people the secret keeper tells, can know and interact with the hidden room. People who've been informed by the secret keeper can't, even if they want to, tell other people about the room.' Mezrielda gestured in the general direction of the door hidden behind the armchair and ferns. 'When you went into that hidden room you disappeared from my sight, vanished into thin air, because the secret keeper hasn't told me about the room.'

'That's why I can't talk about it or tell you where it is!' Bagsy exclaimed, understanding now, and feeling relieved she hadn't been cursed. 'That's why everyone gets so confused where I've gone when I go to my room…' Bagsy trailed off, finally grasping a context she'd been unaware off previously.

Mezrielda was nodding in satisfaction. 'Sometimes my genius amazes even myself.'

'Alright, Merlin,' Bagsy joked, 'don't get too big for your boots or you'll have to walk bare foot.'

'Don't you see?' Mezrielda went on. 'We need a dark, secluded place that we can guarantee won't be disturbed.'

Bagsy frowned. 'Why?'

Mezrielda lowered her voice to a whisper. 'Once we've collected all the needed ingredients to brew the Animagus potion, that potion needs to be placed in a vial into a dark, secluded space where it cannot be, in any way, disturbed. You have access to a room that no other student can get into, no matter what.' Mezrielda gave a confident nod. 'I think it's safe to say we've solved that part of the Animagus quest.'

Bagsy glanced back at the hidden room. Mezrielda was right – it could definitely be used for that – but that would mean Bagsy would have to stay out of her room for who knows how long and share the dormitory with the other girls. It could be worse, she supposed.

'Who told you about that room?' Mezrielda asked suddenly.

Bagsy paused, casting her mind back to her first year. 'Blythurst. He'd written the room's location on a piece of paper he told me to read it.'

Mezrielda hummed thoughtfully. 'Well, until Blythurst dies, you won't be able to tell anyone where that hidden room is, no matter how hard you want to.'

'It's where I sleep,' Bagsy explained, 'so that I don't have to share a dormitory with other people.'

'Oh, I envy you,' Mezrielda murmured. 'I despise sharing a dormitory. Maisy's the worst, always telling fibs. Not to mention she nearly got me expelled last year when I was accused of stealing her glasses. They're only glasses, why did it have to cause such a fuss? She got them back anyway.'

'She did find them in your trunk. I can understand people's suspicion,' Bagsy offered, then, 'and she may not always be fibbing.'

'Oh?' Mezrielda perked up in interest. Bagsy recalled what she'd seen in Hogwarts lake. 'Interesting…' Mezrielda murmured. 'Remember when you saw Mephit testing the water of the lake?' Bagsy nodded. 'There could be a link there. It's his job to deal with the creatures in and around Hogwarts, after all. Him and Belta Zotova.'

'Maybe we should ask her, then,' Bagsy offered. 'Belta Zotova, I mean.'

'Maybe...' Mezrielda sounded unconvinced. 'But for now, we better get to our lessons.'

Mezrielda had Defence Against the Dark Arts, whilst Bagsy was headed to her day-time Astronomy lesson. That night, from Midnight, there would be Astronomy again, and Bagsy intended on slipping into the kitchen during the lesson to procure the silver teaspoon Mezrielda needed to become an Animagus. Where to get the grass seeds from had puzzled Bagsy at first – the greenhouses didn't have mundane grass seeds, nor did the potions store cupboard. Bagsy had decided she'd need to collect grass from outside and thoroughly clean it to ensure no dew she'd collect from it would have ever seen sunlight or touched human feet.

Come Astronomy, it only took a small nod from Bagsy for Winifred to catch onto what she needed.

'Of course, Bagsy, I'll be riiiiight on that for you,' Winifred breezed, looking around herself. She gave a wink at another Ravenclaw who, as Professor Jones was walking by, quickly stuck his leg out, tripping him. Winifred fell about in laughter as Jones, flustered, dusted himself off and reprimanded the offending student. Bagsy, meanwhile, had already slipped away.

Her spider slippers and gloves easily held to the wall and Bagsy, scuttling along like a bug, quick and quiet, passing over patrolling professors and dozing paintings swathed in the shadows of the ceilings, easily arrived at the kitchens undetected.

Dropping to the floor, Bagsy looked at the painting in front of her. It was of a woman who had a creepy sort of smile and eyes that seemed to follow you. Unlike every other painting in the castle, this one didn't move, and Bagsy found herself grateful for that fact. Suppressing an intimidated shudder, Bagsy pushed the painting open to reveal the hidden kitchens. She tiptoed inside and began opening and closing drawers. One of them had to contain cutlery – it was just a matter of time.

'What is miss doing here?' a small, squeaky voice asked. Bagsy jumped out of her skin, dropping the spatula she'd been holding as she'd rummaged through a drawer. 'Oh, so sorry, didn't mean to startle miss, no,' the elf said pleasantly.

Bagsy sighed in relief. 'Horba,' she greeted him. He had helped Bagsy and Mezrielda escape the blood eyed beast at the end of their second year.

'What is you doing here?' Horba asked. 'Miss is making a mess of the kitchens.' He didn't look pleased.

'Oh, I'm so sorry!' Bagsy exclaimed, picking the spatula up and placing it back. 'I'll just be on my way…'

Horba tilted his head in interest. 'What is Bagsy looking for?'

'A silver teaspoon,' Bagsy replied.

'Why?'

'I'd… rather not say…' Bagsy squirmed under his gaze.

Horba blinked and nodded with a smile. 'Horba owes you his life. Horba can spare one teaspoon.' The elf opened a small drawer a few paces away from them, deftly throwing it to Bagsy. It was a tiny spoon and moved at an incredibly fast pace. Instinctually, her eyes following its path, Bagsy easily caught it out of the air. Horba narrowed his eyes. 'You are not like the others miss, do you know this?' Bagsy stood very still, regarding him nervously. What did he mean? 'Your magic…' Horba trailed off. 'It is different.'

'I better get back to my lesson,' Bagsy rushed out, feeling uncomfortable. She didn't want to talk about her magic, so she didn't wait for Horba's response, and quickly exited the room.

Bagsy easily slid back into the Astronomy lesson, silver teaspoon safely in her robe's pocket.

'Everything go according to plaaaan?' Winifred asked curiously, her legs kicked out wide as she reclined lazily in her chair. She clearly hadn't bothered to look in her telescope all lesson.

Bagsy nodded, returning her attention to the class. She didn't want to fall behind and add Astronomy homework to her growing pile of errands. Professor Jones let her off extra work so long as she maintained her grades.

At breakfast the next day, Bagsy slipped Mezrielda the spoon.

Giving her a curt and approving nod, Mezrielda stowed it in her robe. 'Impressive work,' she praised. 'We're making good progress. But I have to ask… how is the weather machine coming along?'

Bagsy gulped. 'To be honest, Mezrielda, I hadn't thought about it at all. Can't you just wait for an electrical storm instead?'

'I could,' Mezrielda admitted, 'but it would make the process incredibly difficult, and increase the risk greatly. The longer there is between the final steps of the potion and the actual transfiguration itself, the more scope for mistake there will be. If we make an error, Basgy, it could go horribly wrong. I could end up disfigured, or gravely injured.'

'Oh…'

Mezrielda frowned. 'Indeed.'

Bagsy wanted to tell her how busy she was. She'd stayed up all of last night working on Tod's cure, her homework, and the Hufflepuff brooms given they were to face off against Slytherin in a week and a half. But she had told Mezrielda she'd help her become an Animagus, and she didn't want her friend to think she was going back on her word, nor did she want her friend gravely injured. Mezrielda could trust her – Bagsy had to make sure of that. That was one of the many uses of exhaust-gone. It allowed her to keep up, or at least get close to keeping up, with everything she said she'd do for her friends.

Double Defence Against the Dark Arts was with the Ravenclaws on a Thursday morning, and Bagsy found Winifred surprisingly gravitating to her side during the lesson, squeezing into a seat between Bagsy and Itsuki.

'Hello,' Bagsy said uncertainly as she took notes. Professor Fitzsimmons was giving a lecture on the Nuckelavee, a rare water dwelling beast, that was a horse with a man's torso merged onto it's back. Instead of a face, it had only a pale white mask with down turned black eyes, and apparently had an affinity for lightning. Even looking at the ancient cave drawing of the creature printed on the lesson's handout sent shivers down Bagsy's spine. Below the mask it had a singular, bulging eye.

'Hiiiiya,' Winifred breezed as she rifled through the pages of their textbook. They had been given a hand out for this lesson, and told they wouldn't need the textbook, and Winifred's expression was slowly turning into a frown as a result.

'It's odd, isn't it?' Bagsy murmured, guessing she was thinking the same thing. It was abnormal for them to stray from the textbook.

Winifred nodded. 'Yeeeah… I didn't reckon we had the Nuckelavee on the syllabus this year. It's way more advanced than what we're uuuusually given.' Winifred slammed the book shut. 'Nope. Not a page on it in the third-year book.'

'Odd,' Bagsy repeated.

There was a sudden bang and the students whose attention had been drifting, Bagsy and Winifred included, turned to the front of the class to see Fitzsimmons standing, hands smouldering where they'd clapped so hard it had sent a shockwave through the room.

'This is vital, please pay attention,' they said in a very quiet voice so that the class leant forward in their seats. 'There are two kinds of Nuckelavee. Both are as deadly as each other, and should you ever encounter them, you must hide. You cannot outrun them. You will not be able to kill them. No. Hiding is your only option. But…' Fitzsimmons began pacing from side to side, a trail of dark green wisping out of their wand and forming the grotesque figure of a half-horse half-man Nuckelavee, its arms elongated to reach the floor easily as the torso sat tall upon its back. 'Nuckelavees don't feel pain from heat or cold or even being hit directly by a lightning bolt. They have a keen sense of smell, a sharp mind, and a patience like no hunter before them or after. They will most likely find you. This is where you must figure out what of the two kinds it is. If it is a fresh water Nuckelavee, salt will deter it, and perhaps save your life.' Fitzsimmons paused, their eyes raking across the class. 'If it is a salt water Nuckelavee, any salt-less water will do the same. Be sure to think what kind of Nuckelavee it is and be sure to have said provisions on yourself should you ever face one.'

'Creepy,' Winifred murmured, 'but I bet I could give it a run for its money…' Winifred winked at Bagsy, making a soft sizzling noise and imitating fire with her fingers. Bagsy wondered what would happen is Winifred faced a Nuckelavee, or even, the blood eyed beast. Winifred seemed, in some ways, unkillable. If she was injured she simply lit on fire and healed. Could anything truly hurt her?

During free period that evening Mezrielda had Defence Against the Dark Arts again, as did Tod, but he had chosen to skive. Bagsy had shot him a meaningful look at lunch when Mezrielda hadn't been paying attention, and her meaning had been plain.

It's done.

Last night Bagsy had done more than just work on Tod's cure; she'd finished it.

Now, cuddled up next to the window overlooking the lake in the quilt her sister had made her, Bagsy waited for Tod to arrive. She was wrapping up the risk assessment for the Herbology practical they'd be beginning tomorrow. She'd barely finished writing the last words when Tod was standing before her.

He flicked his head, swishing his dark hair out of his eyes, and shot her his crooked smile. 'Let's see it, then,' he said. Bagsy unwrapped herself from the quilt, supressing a shiver in the cold library, and produced a tall, thin vial from her robe. The liquid was a pale, opaque grey. 'Impressive,' Tod murmured, taking it gingerly from her. 'And this won't kill me?'

Bagsy shook her head. 'No. I isolated what ingredients were forcing the innate abilities to be over worked and replaced them with stuff that's used to replenish or restore. You know, like how snake fangs can restore clear skin, or strength, or even energy when used in other potions.' Bagsy had the wideye potion and exhaust-gone to thank for her break through – she'd theorised that ingredients which brought back energy, like snake fangs, could also bring back other things. From there, it had been a case of trial and error.

Tod popped the cork off and sniffed the mixture. 'It's now or never, I suppose.' Bagsy's heart stalled as Tod tipped the potion back, drinking the whole thing in one go.

His head lurched forward, a grimace across it. 'Yuck,' he said, making a face and sticking his tongue out. 'Not the most pleasant, I'll admit. But if it works I won't complain.'

'The effect should be almost immediate,' Bagsy explained.

Once, when Bagsy was little, there had been a mouse loose in her home. Florentchia and Himble hadn't bothered to deal with it, but Bontie had set a mousetrap. When Bagsy had seen the poor animal trapped the next morning, injured beyond repair, she had begged Bontie to never set another one. The idea of being that poor little creature, unable to escape, hopelessly helpless, small, weak, and at the mercy of more powerful beings, was horrific to her.

When Bagsy felt a sudden push of cold around her in the library she knew, on some level, exactly what that mouse had been feeling. 'Tod…?' Bagsy asked cautiously, not liking the sudden expression of dark concentration on his usually breezily confident features.

His crooked smile was gone, and his shaggy dark hair hung dangerously in his eyes. 'Bagsy,' he spoke, his voice a sharp icicle in the cold space. 'You don't remember what I told you about my power, that I can alter memories and opinions and feelings, that it drains my energy to do so, and that if I overdo it, it can kill me. You will forget all of these things.'

'Tod, please,' Bagsy begged, feeling parts of her brain melt away like ocean waves, slipping between her frantic fingers. 'Don't take my memories!'

The dark expression on Tod's face only became more strained and sinister. 'I'll make you forget more unless you write down exactly how you brewed this cure,' he threatened, his fists clenched at his sides. Bagsy stared at him, dumbfounded. 'Fine,' he growled. 'I'll start with your memories of Mezrielda, seeing as her friendship is so precious to you,' he spat jealously.

'Okay!' Bagsy blurted, scrambling for a pen and paper. 'Okay, okay, Tod, I'll write it down!' Bagsy took out her messy note book and quickly scribbled the process, including what ingredients to add, in what order, and in what amount, as well as what ways to stir and how long to leave it for. Once she was done, her hands shaking, she tore the page from the book and handed it to Tod.

Tod scrunched it up in his hand and shoved it into his pocket. 'That wasn't so hard, now, was it?' he grumbled, his expression losing some of the scariness it had held. Bagsy felt another pulse of cold and wrapped her arms around herself, looking up at Tod miserably. 'You don't remember how to brew that potion anymore,' Tod hissed. Bagsy nodded glumly, feeling the words and instructions turn into mist inside her brain. It was like her head was a cauldron, and Tod was poking a long pole into it, stirring the mixture around, plucking parts out and replacing them, re-arranging what he left behind. It was very uncomfortable, but there was nothing she could do about it. 'So Mezrielda did lie,' Tod breathed, his shoulders sagging in relief. 'The cleanse you made in first year – it hasn't made you immune. It only returned memories I'd already taken. Well, if that's the case,' Bagsy was shivering at this point so the third push of cold simply moved over her skin like ripples in a pond, 'you don't remember how to brew that potion, either.'

Bagsy hung her head, defeated. She couldn't even write to her sister for the instructions to brew Silver Cleanse again, her owl still only flew out over the lake, as did the other owls she'd tried to use. 'How could you?' Bagsy whispered in a voice so quiet she was half-hoping Tod wouldn't hear.

Tod was silent.

Abruptly, Bagsy was on her feet, the chair she'd been sitting on clattered to the floor. Tears were filling her eyes but, for once, she found it was a hot volcano of anger bubbling inside of her, not fear. 'How dare you,' she hissed, an animalistic fury filling her voice. 'I help you, and stay up night after night researching and preparing and investigating, and this is how you repay me? Do you think I'm so untrustworthy that you have to meddle with my own mind? Steal from my own memories?'

Tod took a step back as Bagsy took a step forward, a flash of panic on his face. Clearly, he was as surprised by her outburst as she was.

Without a second thought, Bagsy found her hornbeam wand in her hand and pointed at Tod. 'What kind of a friend does that?' she growled, baring her teeth. 'Who do you think you are? I trusted you!' Bontie's warnings echoed in her head – she'd told her not to trust Tod, that someone with such powers would take advantage of others and couldn't ever be a friend; that he was someone she should stay far away from.

Bagsy saw Tod's eyes flash down to Bagsy's wand, his panic subsiding. They both knew there was nothing she could do with it. Yet, somehow, the simple action of pointing it at him had conveyed exactly what Bagsy was feeling. They both knew it. Whatever friendship they'd had was done.

'You should forget we ever had this conversation,' Tod murmured dejectedly.

A feeling of pure revulsion spasmed through Bagsy – was he going to take her anger away from her, too? Make her forget his betrayal? Yet, as Tod turned and walked calmly away, Bagsy felt no more chills surrounding her, nor anymore poking in her mind. He'd decided to leave her with the bitter taste of his betrayal, then.

Bagsy slumped back onto the windowsill, not bothering to pick up the knocked over chair from the floor. The living stampelia's flowers seemed to reach towards her, as if to give her a comforting embrace, their petals changing to a light blue that only made Bagsy feel worse.

How could he?