Professor Babbling instructed that I stay behind after class. So I pulled off my backpack, gestured to Terry to go ahead (we had become close friends in our constant experimenting, even after I had returned to living in the Slytherin dormitory), and dropped the backpack - navy and yellow - onto the table. "Yes, professor?"

"You are very much advanced compared to the others in the class," she said slowly, looking at me carefully. "So I thought I'd make the offer I make every year to such students - would you like to learn at a more advanced level?"

Ancient Runes, despite the fantastic teacher, was indeed boring because I was ahead of the class, and knew how to undo all the runes on every practical, such that I had taken to experimenting with my own runes while letting the others have a go at it, although my projects were, admittedly, going nowhere.

"Yes," I said at once. "Thank you, professor."

She shook her head. "It's my pleasure."

I walked out of class with a light heart, and even the Cruciatus casted on me by Goyle did not remove the happiness and excitement I felt about going on an accelerated Ancient Runes syllabus.

That evening, I stood in front of the DA. "You guys are doing plenty well in duelling, it's fantastic to see your progress. But we'll be doing something different today. It's easy to duel, to meet something head on, to fight something you can see. It's harder when you can't see the person shooting spells at you. To test your reflexes, I would like you to form pairs, and I will Disillusion one of the two of you, and the person who is Disillusioned will do your best to land a spell on your partner. The other person will do their best to block and to incapacitate the invisible. I'll show you an example. Ginny, do you want to be visible, or invisible?"

"I'll be shooting spells at you," she said with a grin, and I tapped my wand over her red head, and she shivered. Then I took the end of the stage, and no doubt she took the other, though I couldn't see her.

I waited a very long time, as patiently as I could, though keeping my eyes sharp for the telltale light. Ginny was excellent at nonverbal spells, which made being invisible the perfect element for her. But I had been training since I was eleven with one of the best duelling instructors of all time, and I kept my breathing light, my ears acute, my eyes sharp, not at all disheartened by the long wait, which I thought was a smart move by Ginny.

Then the first light snapped out at me. I quickly aimed a spell in that direction, before blocking the spell she had sent at me. I was pleased to hear the sound of something hitting the ground, although the spell hit the mirror at the other end of the room of requirement and cracked the mirror. Then I saw a dozen spells shooting at me from all directions, and I knew she must be ducking and weaving very quickly on the other end. Standing my ground, I easily created a specialised protection charm and expanded it to block all the spells, before dropping it the moment the last spell hit.

A bright blinding light came from the other end, and I knew she was trying to blind me. Tapping my glasses, I switched it to sunglass mode and shot a spell in the direction she had come from. It collided with another red spell she had shot, that exploded with a shower of sparks. But she was smart, and there was a second spell hidden behind the red light. I ducked, feeling it whistle right above my ear, and collided with the wall at the back with a loud bang.

The bright light stopped, but I kept my sunglass on, even as I tried to listen for where she might be. I heard the magic right before she could finish her spell, and instantly casted an armoured protego that protected my entire body, preventing any spells. Then, certain I knew where she was, I sent a number of blasting curses at the ground, intentionally forcing her into a small corner at the back, where with a flick of my wrist a golden web fell upon her, and I casted the expelliarmus to disarm her before using the finite to reveal her presence.

But there was a something sharp pressed into the small of my back. As I watched, the "Ginny" in the web faded away, and the wand I had retrieved from her turned into a twig.

Laughing, I began to hold up my hands, but then dived for the ground, turning on my back to shoot a spell at her, deflecting her first spell and then disarming her in quick succession. Her wand shot out of her hands, straight into mine.

"Impressive, Ginny," I said as I stood, clapping, hearing the entire room cheering along as well. "How did you manage that?"

Ginny glared at me balefully, her hands outstretched for her wand back.

"A window that allows the spell to go through there and come out on the other side," she said. "I was behind you all along."

"You wanted to lure me into a false sense of security. But you waited too long. You could have ended it sooner. And the battle is never won until the other person is without wand."

Ginny sighed. "I suppose I deserved that."

"You'll need to teach me that window spell, though," I told her on no uncertain terms. "Anyway, you lot, pair up. And those whose pairs don't have a person who can cast the Disillusionment, raise your hands so I can cast it."

"You would have won me if we were both Disillusioned. This fighting style is hardly fair," Ginny mused thoughtfully as she watched the DA members get started on the exercise.

"Well, when you're fighting wizards more than twice your age, there's no such thing as fair," I said. "It's about making the best of what you have, being creative with your small arsenal of weapons, polishing your usage of them to perfection. No use having a huge bunch of spells in your head that you don't know how to use well. But you still have to teach me that spell. That could be useful for more than just the way you used it. For passing messages in class, stuff like that."

Ginny's eyes lit up. "Good idea. It's in this book...Illusions and window charms. Innocent looking, but pretty cool. I'll pass it to you by owl when I get back to my dorm. You can modify it, can't you?"

I paused. "I'll need to see what it's like, first. But most likely, yes."

I stopped by Millicent and Carrie, the latter Disillusioned and shooting spells, and the former trying to pinpoint her location using rocks and other Transfigured objects. I nodded, pleased with that fantastic idea, and moved on. Tracey was paired with Rose, and Tracey was blocking well. She grinned at me as I passed, raising her brows, and I shook my head, smiling a little. Things had gone back to normal between us after she moved into the Room of Requirement. The Carrows were furious that yet another student was missing, and had interrogated everyone in Tracey's dorm, including me. But I had powerful occlumency and the ability to promptly vanish anything that I did not like (alcohol in punch, veritaserum in tea, that wandless spell was dead useful), and the others were not on the plan and genuinely didn't know, though Daphne did weep and we had to comfort her in our dormitory together (I felt a little useless sitting there trying to show support, but ever since I had been slipping her little bits of parchment), so nothing was revealed to the Carrows, and Tracey had been in the Room ever since.

I passed by what looked like army barracks, with hammocks and blankets and personal trinkets scattered all over. The room was getting increasingly large by the day, with more and more students being delivered to the Room once news via Potterwatch of whose parents were targeted and why were heard. In fact, most of the DA were now forced to secretly sneak hampers of food from the kitchens up to feed the students, but it was hardly enough food because we could not afford to make our asking of food to obvious, or the Carrows would catch on. We couldn't even collect the foods at mealtimes, often having to wait until odd hours when we were certain no student in their right mind would be in the kitchens at that time to collect the meals discreetly.

I was working on communications, and an idea struck me. I could use Ginny's spell, couldn't I? That would save a fair amount of time. But I wasn't sure if food could be passed from one window to another. It would need to be tested. Would nutritional value of food still hold when passed through the windows?

"Oi, watch out!" But even before the warning, I was already deflecting the errant spell that went my way. A short Hufflepuff boy was grinning sheepishly, and I shook my head but waved a hand to get them to continue, as I progressed down to watch the fights. True enough, Neville's wand movements had been sharpened plenty since the day I met him fight, and the Carrows had started humiliating him in the same way they enjoyed humiliating me - by making Neville suffer the Cruciatus from people who disliked him, like Crabbe and Goyle and Nott. I had begun to teach him how to lessen the effect of the Cruciatus too.

My clock chimed, and I told everyone to keep up the good work. "Head in different directions, please. And make sure some of you use that passageway the Room conjured," I told them. That passageway was dead useful, popping the students directly in the castle, but to random parts so that not everyone who exited it went to the same place. "We don't want the Carrows to wonder why there are so many people coming from the seventh floor."

"Bye Cass," someone yelled.

"Thank you, Cassie!"

Hearing their voices praise me was music in my ears. I waved them goodbye, then held back with Ginny, Luna and Neville, informing them of my new idea about the food. Aberforth had begun to complain that he had little left, and something had to be done about it, after all. Ginny promised to send the book and help out with the experimentation. Then I bade them goodbye and headed off to Professor Snape's office for Alchemy. The timing changed all the time, and today he had scheduled it for four on a Saturday, so that's when I met with him.

He was sat in his Headmaster's chair when I arrived, and nodded a greeting. "Have you managed to complete your assignment?"

I nodded, passing the five feet scroll to him.

He flipped through, and nodded briefly before lifting up something in his hand - a heavy golden ring.

"This was not originally a ring, but turned into one. Most of the goblins' gold are like that, actually. In fact, all our galleons are alchemical gold," he said.

I nodded. I was aware of that. There was no way there was enough real mined gold from the earth to create so many galleons throughout the Wizarding Worlds. Although I did know some countries used different forms of currency, other than alchemical gold...like China used round nickel coins with a bit of jade to seal its value, and a hole in the middle so that it can be easily strung up and brought around on your person, and MACUSA purportedly also uses other forms of metal...

"I would like you to find out what it was originally, and change it back to its original form. It's owner would like it back the way it was."

Frowning at that strange comment, I took the ring, weighed it in my hand. It was heavy, but that meant nothing. All alchemical gold was heavy.

"Work on this. In the meantime...the Carrows and I have somewhere to be tonight, so I expect this properly returned to normal after Christmas break, is that fine with you?"

I nodded, and took my leave, recognising a goodbye when I heard one. The moment I left his office, however, I casted a nonverbal, non-corporeal patronus, and sent it on its way.

Then I settled in a corner to study the ring, wondering how to best approach it.