The Law of Equivalent Exchange

It was a beautiful Sunday afternoon, and yet, Oleandra and Tracey were stuck sitting around a table inside the dank Slytherin common room, staring at a piece of metal that was obstinately refusing to change colour.

"Do you want to have a go? I don't think this is actually possible," Tracey sighed. "We've been at it for hours, and I still haven't got started on that essay on nonverbal spells for Professor Snape..."

Oleandra and Tracey always got together to complete their homework, but since Oleandra had missed most of Saturday's Alchemy class, her input consisted mostly of watching Tracey struggling to transmute gold into lead and occasionally offering encouragement.

"Oh! Look!" said Oleandra, giving Tracey's shoulder a tap. "Something's happening!"

The gold nugget Tracey had placed in the centre of her alchemical circle gradually turned translucid… before abruptly winking out of existence.

"That just means we're out of time," explained Tracey. "The nugget's actually Leprechaun gold. It only lasts a few hours before you need to Conjure some more. Here, I'll take care of it…"

Interestingly, since Leprechaun gold shared real gold's properties, it could be Transmuted into something else, which would somehow cause the illusory substance to 'forget' that it wasn't supposed to be real. Oleandra couldn't wrap her head around how Transmutation could force a temporarily Conjured magical construct to continue existing under a different form permanently, but somehow, it just worked…

"It might be time to ask Theo for help," said Oleandra, discreetly checking her watch. "Or, you know, we could spend the rest of the night banging our heads against the wall."

As the heir to the noble Nott legacy, Theodore had been immersed in the world of Alchemy since his youth. Since Oleandra wasn't on bad terms with him, surely he wouldn't mind giving her a few pointers…

"But…" said Tracey, looking slightly distraught as she flipped through her handwritten notes. "I thought we'd figure this out… together…"

As always, Daphne was nowhere to be found, so Oleandra wasn't expecting much help from her older twin's side. Since Tracey's talents clearly lied elsewhere, Professor Dumbledore's homework would probably remain unfinished until Oleandra could find someone to teach her what she had missed in class.

"Let's go find him," said Oleandra, as she stood up from her seat. "I think I saw him heading downstairs earlier, so he must be in his room."

Oleandra helped Tracey gather up her belongings, and together, they headed for the boys' section of the dormitories. While boys were barred from entering the girls' section, there existed no such restriction for the girls, as Hogwarts's founders had always found girls to be more worthy of trust.

"There it is," said Oleandra, pointing at a nameplate as they walked down a narrow corridor. Near the end of the corridor, there was a plaque inscribed with the names, 'Nott, Theodore,' and 'Zabini, Blaise.' "Theo, are you in there?"

Oleandra knocked on the door and waited, giving the room's occupants the chance to make themselves presentable, and a few seconds later, the door opened a crack, and Theo popped his head out through the opening.

"We need help with our Alchemy homework," said Oleandra supplicatingly, batting her eyelids at him. "We really need you, Theo…"

"Do you know about Alchemy's most important principle?" answered Theo without missing a beat.

"Er…" said Oleandra haltingly. "I was actually hoping you might be able to teach us about that…?"

Oleandra was drawing a blank— of all the things Theo could have said, she hadn't been expecting anything other than a yes or no answer, or a variation along those lines. By hook or by crook, through beauty and guile or through intimidation, she was used to getting what she wanted, but Theo was a researcher at heart.

Only one thing could motivate him!

"Alchemy's most basic principle is Equivalent Exchange— you must give up something to obtain something else. In other words, there's no such thing as a free lunch," explained Theo. "Give and take— I have something you want, and you have something I want— so let's trade."

Equivalent Exchange was something Oleandra understood very well.

"For a gift is always rewarded, and a boon always demands a return…" murmured Oleandra. "If I'm not mistaken, you need my help to draw an alchemical circle— isn't that right?"

Oleandra had gleaned a few insights on Alchemy from Tracey's pitiful attempts to turn a piece of gold into lead. Three things were required to initiate a Transmutation:

An Alchemical Reagent to 'loosen up' the reactant, such as Albedo, Nigredo, Citrinitas or Rubedo.

An Incantation, to be repeated over and over during the Transmutative process.

An Alchemical Circle, to stabilize and guide the reaction to its desired end.

In other words, Alchemy combines Potioneering, Transfiguration and Study of Ancient Runes to achieve the magic of Transmutation.

"We Notts employ a qualified Runesmith to craft Alchemical Circles for the family business," said Theo, opening the door to his room to let Oleandra and Tracey in. "A different Circle is used for each specific Transmutation— for instance, the Circle for the gold to lead reaction isn't the same as the one required to change Platinum to Palladium."

Theo coughed.

"Unfortunately, the Runesmith in question is now facing a life sentence in Azkaban, so I've lost my custom Alchemical Circle carver," he explained. "Help me with my experiments, and I guarantee you'll learn more about Alchemy than by simply attending Dumbledore's class. Win-win, right? So, what d'you think?"

Theo extended his hand towards her.

"It's a deal," responded Oleandra, taking Theo's hand and shaking it. "Incidentally," she added as an afterthought, "what exactly are you working on, right now?"

"Time," said Theo enigmatically, producing a stolen Time-Turner from his pocket. "I need your help to refine Sands of Time."

Oleandra's expression immediately turned ugly— why hadn't she asked about his experiments first, before sealing the deal!? Time magic was tricky business, and unless one was very careful, this type of magic was liable to rend the timeline itself…

"I knew this was a bad idea," said Tracey disapprovingly.