It didn't take longer than ten minutes for Dumbledore and McGonagall to appear, Madam Jeffries in tow, but to Cassie it felt like an eternity. Carefully, biting back tears of pain and fear and grief, she untied the bed hanging from Mary's neck, and tore the pillowcase from one of the pillows and began shredding it. The few strips that weren't smeared with her own blood from her freely bleeding hand, she used on Mary.

First, the deep wound on her left leg - she tied a strip of pillowcase tightly above that - and then the one on her forearm - another tourniquet, and a strip of pillowcase wrapped as a bandage around it - and the remaining wounds she simply applied pressure to.

She had tried to remember a healing spell and couldn't, and felt a tide of panic rising from her chest up to her throat, but swallowed hard and began her Muggle first aid instead. She was methodical, and kept her focus clearly on each task as it came.

As soon as Madam Jeffries' deft hands reached in and began casting healing spells, Cassie felt her limbs go weak and her head begin to spin with images of glinting silver and rivulets of crimson blood on pale skin. Her stomach lurched, and the sudden appearance of McGonagall's steady arms giving her some support were the only thing that kept her upright.

"Miss Derehart needs the hospital wing too, Binty," McGonagall said, "she's in shock."

"Allow me, Minerva," came Dumbledore's serene voice from behind her, but Cassie couldn't drag her eyes away from the tangle of naked bloody limbs lying on the bed. At least the bedspreads were red, she found herself thinking, as a bubble of hysterical laughter escaped her tight throat.

That first shrill, manic giggle opened a floodgate, and Cassie couldn't hold in the laughter that burned the back of her throat and forced hot tears from her eyes.

"Albus, her hand, too," McGonagall pointed out, holding Cassie's palm upright towards the Headmaster.

"It's alright, Miss Dereheart," Dumbledore said softly, and a sudden cool, pale light washed over her. It seemed to dissolve the hot, hard bubble forcing that humourless laughter from her throat, and eased her rolling stomach.

"Now," he continued, "if you could ensure that the girls from this dormitory are moved elsewhere for the moment, Minerva, and get in touch with Miss Macdonald's family whilst Binty removes her to the hospital wing and sees to her, I will take Miss Derehart to my office."

McGonagall moved to object, but Madam Jeffries was first.

"I already have her wounds treated, Professor - only the one was very deep and thankfully Miss Derehart was quick thinking on that front. But I'm concerned about her being a danger to herself - she showed no signs of being this mentally fragmented before."

"Perhaps," Dumbledore said grimly, "we can keep her subdued until her family arrive."

This either answered McGonagall's question or removed her cause for objection, as she simply nodded and, with a last tormented look at Mary, swept from the room.

"Miss Derehart, do you feel well enough to accompany me to my office, or do you need some more help?"

Cassie's legs felt much firmer than before, and the sickness in her stomach was gone. She couldn't say she was fine by any means, but she felt much less like she was about to shatter into a thousand pieces that no magic could ever repair. She gave Dumbledore a nod.

"Good, good," he said, his voice as smooth and calm as ever, and the pair began the long, slow walk to the Headmaster's office.

Cassie counted her footsteps as she followed in the Headmaster's wake. One, two, three, four. Seventeen, eighteen, nineteen. One hundred and thirty three, one hundred and thirty four, one hundred and thirty five. It felt a little like casting a Patronus, focusing intently on one thing to drive the darkness out. But between her strange dark Patronus and the image of glinting silver and crimson there wasn't room for a happy memory - there was only the rhythm of the numbers in time with her footsteps and the pounding of her heart in her ears.

"Moffat toffee," Dumbledore told the gargoyle outside his office conspiratorially, and Cassie noted with surprise that they were already at their destination. Not even a thousand steps. How small Hogwarts was, when you thought about it like that.

They climbed the stairs into the room Cassie had been sent to on so many occasions before. It was almost funny how scared she'd been on more than one of those times that her Hogwarts career might be over; now, when she had done nothing but try to save her friend, she almost wished that she was being sent away from here.

"Miss Macdonald is receiving the best possible care, Miss Derehart," Dumbledore said as he took a seat behind his wide desk, "but I'm sure you've realised that is not why we are here."

Cassie looked up sharply, meeting Dumbledore's piercing blue eyes. This wasn't about Mary? This wasn't about the bite of metal and soft dribbling of dark red blood?

Then… her Patronus?

"You are a clever, talented young witch, as I'm sure your teachers have been telling you for a number of years now - partially in the hope that it would change your focus from silly pranks to your studies, but mainly because it is quite true. Particularly in Charms, as Professor Flitwick delights in sharing with the rest of the faculty."

He wouldn't when he heard about that Patronus though.

"You wouldn't be quite as good at Charms - or quite so good at causing disasters in Transfiguration - if you weren't also magically powerful. And whilst having more power than average is a definite advantage, there are also times when that power can cause additional problems for you."

Cassie swallowed hard, and took a deep breath.

"I'm sorry, Professor. I didn't mean to do it. I had no idea I could do it. I definitely never intended to hurt anyone!"

She felt hot tears building at the back of her eyes and catching in the back of her throat. But Dumbledore just watched her intently for a long moment before rising abruptly to his feet and strolling towards a large, ornate cabinet on one side of the room. Cassie watched him, confused, as he opened the cabinet and drew out a glass orb, flattened on one side so that when Dumbledore sat it on the desk between them, it did not move. What did move, was the swirling rainbow mist inside it.

"That's not a Remembrall," Cassie stated, but her gaze was questioning as she met Dumbledore's gaze.

"No, it's not," Dumbledore replied with a soft smile, "it's an experiment of mine."

He opened a drawer on his desk, and, after whipping a flowery handkerchief from the depths of his robes, picked up an object from the drawer. He held out his hand to display an old, brass spyglass engraved with runes that flowed over its surface like droplets of water.

As soon as the spyglass was displayed, the swirling rainbow mist began to rage like a storm, and the colours darkened until they reached an ebony black. The reaction was sudden and dramatic, and Cassie's eyes widened.

"This spyglass was cursed by a Dark wizard - I wouldn't recommend touching it with your bare skin, let alone looking through it. I haven't quite managed to lift the curse as yet, but it makes for a good demonstration of my Dark magic detector, which I like to call the Revealall - I did rather unashamedly base the design on the Remembrall after all."

"A Dark magic detector?" Cassie asked, confused.

"Yes," the professor said as he wrapped up the spyglass again and deposited it back in the drawer before closing it, "You can see that it has a clear and instant response to Dark magic. Now, if you please, you could hold your wand up beside it?"

Cassie reached into the pocket of her robes and pulled out her wand. She tentatively held it out towards the Revealall, which didn't even flicker.

"You can see that there are no traces of Dark magic around your wand, which would certainly be the case if the apparition you produced was a product of such."

She nodded, but put not entirely trustingly. Dumbledore watched her for a moment, his expression considering.

"Let me pose a question to you, Miss Derehart," he said after a long moment, leaning back into his chair and clasping his hands in front of his belly, "When young witches and wizards spontaneously use magic prior to beginning at Hogwarts, is it their fault?"

Cassie shook her head.

"Why not?" he asked.

"They can't help it. They haven't learned to channel their magic, and when their emotions overwhelm them it's too much for them to control."

Dumbledore smiled.

"Magic does have a tendency to happen by instinct when our emotions are overwhelming. And the more power one has, the more likely it is to be difficult to control."

Cassie looked sharply at Dumbledore.

"It's not the same. I'm a seventh year - I should be able to control my magic by now! I'm not a child."

Dumbledore's smile turned sad.

"The Patronus Charm uses our happiness as a weapon against beings who thrive on our worst emotions. If our negative emotions are strong enough, and our magical power great enough, negative emotions can also be forced into the same mould and produce an unhappy equivalent - one that would not protect us from Dementors. And when those negative emotions are overwhelming, a powerful witch or wizard might make that leap instinctively - particularly if she were already proficient with the charm itself."

Cassie still looked dubious, but Dumbledore's explanation made sense.

"Still, I could have hurt someone, Professor," she said plaintively. Dumbledore shook his head.

"Just as your Patronus cannot affect humans, neither can your alternative apparition. Although I do understand Professor Archer was given rather a shock."

There was a pause, and Dumbledore gave Cassie a look of scrutiny.

"However, despite my complete confidence that what happened was both an accident and harmless in the grand scheme of things, I would request that you take this opportunity to go home early for the holidays."

Cassie felt like she had been punched in the stomach - all the air left her lungs in a whoosh and she couldn't draw in any more, and nausea instead filled the back of her throat. Sending her away from Hogwarts?

"This is not a punishment, Miss Derehart. You have undergone several traumatic experiences now this term, and I believe you need time to recover."

Dumbledore hesitated a moment.

"I say this particularly because I am hoping you might be able to help me next term, as you offered to me during your stay in the hospital wing. And to do so, you need to recover - and I hate to admit it, but I don't believe Hogwarts is the best place for you to do so at present."

"This… definitely isn't a punishment? You don't think I'm… weak?"

"Absolutely and completely the opposite. But every injury needs time to heal - those of the heart and the head no less than of the body."

Cassie nodded, slowly, her eyes filling with tears.

"Ok, Professor. I'll go."

It was a difficult farewell between Cassie and her friends before her trip back to her family home. With Mary's breakdown and Cassie's sudden departure, there seemed very little for the Gryffindors to get excited about despite the approaching festive season. In fact, the prospect of saying goodbye must have been more than Sirius could bear - he was conspicuously absent from the gaggle of teenagers gathered in the Entrance Hall as Cassie's trunks were loaded into one of the horseless carriages for the trip into Hogsmeade.

"Promise you'll write to me as soon as you're home," Lily said in a rush, crushing Cassie to her.

"Yeah, you aren't getting out of the Christmas party even if you're getting out of end of term," James added, pulling both girls into a large hug of his own.

"Pile-up!" Peter exclaimed, and the others all piled into a big group hug - some arms held on desperately, whilst the grips of others seemed leeched by sadness.

"I will write to every single one of you, and I expect to hear absolutely everything that happens here. Except, and that means you two, Moony and Lils, for homework - I am purposefully not reminding any teachers of this fact so don't you dare land me in it."

There were a few half-hearted laughs and some sad smiles, but the effort to be cheerful was clear.

Cassie was barely home for a week before the first letters came by.

Dear Cassie,

Hagrid has really outdone himself with the Christmas decorations this year - but they aren't quite the same without a Dizziness Charm carefully applied to the big tree next to the Slytherin table I must admit…

Dear Sparks,

I've been thinking about your prank on Padfoot - we need a fresh approach. Moony and I can act as consultants at the party. Speaking of which, a bet is a bet and I'm hosting - and you and Moony are picking out mine and Padfoot's outfits, so best rip the plaster off quickly…

Dear Cass,

PLEASE let me come and visit you over the holidays - I can't handle my mum being my mum AND the extended McKinnon clan all crammed into the house at the same time for two solid weeks!

Dear Cassie,

We're really missing you here - Sirius is being even more of a git than usual, James is spending all his spare time with Lily, and Remus is nose-deep in a book 24/7. It's very boring, and I can't find more than 3 ways of applying Cheering Charms to foodstuffs without you to help…

Dear Sparks,

I take it you never found out what caused your Patronus to react like that? It's incredibly interesting and I haven't found a single reference to what might have caused it even in the Restricted section…

However, it was very noticeable that one member of the gang did not send a letter. To start with, Cassie felt hurt. She thought that she and Sirius had made up, and the strange, tense quality their relationship had taken on had been diffused at last. But apparently not.

After the second week, she started to get angry. How could he? What sort of friend wouldn't even write after what had happened? He obviously didn't care at all. So much for being friends again properly.

It didn't help that Cassie's mum was being far more difficult than usual. Cassie knew her mum's job at the Department for the Regulation and Control of Magical Creatures was a tough one, and could very very stressful and dangerous at times, but her mum was being even more sharp-tempered and strict than usual.

"Don't think you're going out to whizz around on that broom all day again," Antara Derehart told her daughter belligerently over breakfast one particularly windy morning that would have been just perfect for that very thing, "You can at least help by doing some cleaning. Your room is an absolute dragon's lair - how you can have it so cluttered in such a short amount of time at home is beyond me."

Cassie rolled her eyes, but only once she was sure her mum was facing the other way.

"Actually," David Derehart chimed in, giving his newspaper a shake and folding it up, "I was hoping Cassie could pop down to the hardware shop for me. I need some bits and pieces for, you know, DIY."

Cassie's eyebrows rose. Her dad was absolutely terrible at DIY, but her witch mother was so put off by the tools and materials that he had kept up the pretence now for their entire marriage - it guaranteed him, and occasionally Cassie too, some peace and quiet when most necessary.

"Well," Antara replied, sounding a little put out, " as long as she's doing something constructive."

As soon as the loud crack that signalled her mother's departure for work filled the kitchen, Cassie's dad leaned over conspiratorially.

"So, how about tickets for the Magpies game against the Harpies?"

"Dad," Cassie said in all seriousness, "you are absolutely brilliant."

So it was to an empty house that a small, wind-buffeted owl arrived, bearing a very thick envelope addressed to Cassie in sprawling handwriting. The little owl flitted around the house for the space of around half an hour, before eventually leaving the letter in the front porch of the house.

Unfortunately, the little owl hadn't been gone above ten minutes before a particularly strong gust of wind hammered its way into the porch, blowing the envelope into the air and depositing it behind a large plant pot.