In the narrow Knockturn Alley, just around the corner from Borgin and Burkes, two figures stood huddled together against the dark brick wall.

There was nothing unusual about this from afar, as many suspicious people would often be found lurking about there. Even as you got closer - close enough to see who exactly they were - you wouldn't have thought anything strange of those two people stood there in the shadows.

That bode well for them because if anybody was up to something suspicious, it was those two people.

"Worst comes to worst, just grab my hand and I'll apparate us out of there." The woman whispered with a sense of exasperation.

The man stood with her, much taller and broader, sighed with slight irritation and confessed, "But what if they know we're not meant to be here? What if they start asking personal questions that we can't answer?"

"Well that's what the apparition is for." She explained, "All we're doing is buying a sodding book - the guy isn't going to be quizzing us about deeply personal details."

"Alright, fine, let's go and get this over with."

Orion Black adjusted his suit jacket over his shoulders, and ran a hand over the top of his dark hair to smooth it out over his head. He stepped into the middle of the alley and turned back to his wife, "Just so you know, I'm already regretting this."

"It was your idea!" She retorted, following behind as they began making their way down the street, "Besides, I think it's a good idea as long as we don't waste anymore time. This potion won't last forever."

Of course, these two figures were not the real Orion and Walburga Black, for they were still on their extended holiday.

No, these two people in Knockturn Alley, who looked and sounded exactly like Orion and Walburga, were actually Regulus Black and Esmerelda Avery.

"How long do we have left?" Regulus asked as he came to a stop just in sight of the door to the old Borgin and Burkes shop.

Esme cleared her throat and smiled in the kind of way that is not at all comforting as she replied, "Well... Funny thing, that. Given I technically bought the Polyjuice from some guy under a hood down here yesterday, I'm not completely certain about the quality of his brewing."

"Esme!" He hissed, "You never said how utterly unreliable this is!"

"Well, we couldn't wait a month to brew it ourselves could we?" She shrugged it off and brushed past him, making her way towards the door of the shop to push it open.

Needless to say, the two of them had barrelled into this plan - none of the details thought out properly and with little regard for how reckless they were being.

Of course, time was not on their side as they needed to find out as much about horcruxes as they could before the Dark Lord uncovered their betrayal. That, and the fact that neither of them properly wanted to deal with what Antoinette Avery had warned them of, was what had pushed them to action so quickly.

Regardless of how stupid they were being, it was offering a much needed distraction from the fear that at that very moment there were most likely Death Eaters out there trying to track them down and uncover their secrets.

They really were being hunted down on both sides.

"Let's just... Let's get this over with before I really start to panic." Regulus shook his head with a feeling of hopelessness and, as the door pushed open and the small bell rang out to signal customers arriving in the ship, he followed her inside.

Upon entering, it was a large and spacious room - one with tall walls and dust littering every corner and surface possible. Against one wall was a stone fireplace, as dirty and old as everything else in the shop, though it was barely visible around the brimming cases and shelves and boxes filled with all sorts of old artefacts and antiques.

Esme held a hand to her chest and let out a cough - partly to further signal their arrival in the shop, and partly to clear her lungs of the musty air.

"Remember your voice." Regulus murmured into her ear as he moved around her and began browsing through the spines of books that had been rammed together in an enormous bookcase that only just filled the wall from floor the ceiling.

"Right." She nodded, making a mental note to elongate her vowels and sound more southern.

Then, emerging from behind the towers of disorganised items, came the shopkeeper. He looked much older than he really was, already stopping and crooked, as a much older man would be, and his dark hair was already thinning and had been smoothed haphazardly over his pale head.

"Ah!" He recognised the woman at once, "Mrs Black!" he greeted, "What a pleasure to see you again, why it has been quite a while. Do you bring more of your wondrous family history to share with me?"

"Mr Borgin." Esme raised her nose up at the man, "I'm here with my b-husband, of course, and I was hoping to inquire about a rather particular book which I can only hope you have in your possession."

"Of course, of course." He nodded and bowed several times, "What book is it that you're looking for?"

"You must understand, Mr Borgin, that it would be in everyone's greatest interest for this trip to be unspoken of." Esme mused thoughtfully as she peered past the short man before her.

He nodded fervently again, "Yes, of course, Mrs Black."

Then, Regulus came to stand beside her, "This is a very delicate matter." He explained in a low and gruff voice, "And if, for whatever reason, this were to get out, well... It would upset a lot of very important people."

"Y-yes. I understand. It will be undisclosed."

Esme glanced across at Regulus, cleared her throat again, and stated, "We're inquiring about Secrets of the Darkest Art."

"Oh. O-ho." Borgin almost let out a chuckle as a mischievous grin grew across his thin lips. He clasped his hands together in front of him, bowed his head yet again, and sharply turned and disappeared behind ether towers of merchandise again.

"Don't say you told me so, but I don't like this. I don't like it one bit." Esme hissed to the boy beside her, tugging at the tight collar around her neck.

He took a deep breath and straightened up to his full height, "Get the book. Go home. Pack our things. Leave. As long as we stick to that we shouldn't get caught."

"Okay. Good plan. Clear plan. Hush! Here he comes." She whispered, dusting off the front of her dress and resuming her previous cold and stern composure.

And, as expected, the little worn man reappeared before them, having stumbled over an old cardboard box filled with gold trinkets, and presented a large, leather bound book with purple markings engraved all over the front cover of it.

Mr Borgin was practically shaking with giddy excitement as he handed the book to Esme, and took a few steps back.

"It's the only copy I've ever come across in my life. It was never made for the general public, you see." He smiled almost proudly, "It's extremely rare. Worth a pretty penny or two."

Regulus, having visited the shop several times before with his parents, did not like Borgin one bit. In fact, the man rather repulsed him.

"How much?" He asked, coughing to lower his voice some more as he took the book from Esme and turned it over in his hands.

"Well I do hate to part with it, you see. The book being so rare and valuable and all." Borgin's smile faded as he feigned sincerity.

Regulus raised an eyebrow, "You see, this book is of great interest to some very important people. Some people who are renowned experts in the field of Dark Magic... They would know exactly how much to pay for an item like this..."

"Mr Black, I would never dare to question your experience in the Dark Arts." Borgin bowed his head yet again.

After some tiresome bargaining, eventually money changed hands and the two teenagers - still of course looking like Walburga and Orion - stood outside of the shop with Secrets of the Darkest Art in their possession.

"I can tell, just from holding this book, how dark it is." Esme frowned as she flicked through the pages, glanced over the cover again, and eventually pocketed it out of sight.

"I just hope it can tell us how to destroy that locket." Regulus shook his head, "Because if not, then I don't know what to do."

She paused in thought for a moment, then suggested, "We might have no choice but to go to Dumbledore then. I think he's the only one we can trust - he knows where our loyalties lie."

Esme wasn't particularly keen on that idea.

As long as the book included the information that they needed, the two of them could destroy the horcrux and flee to refuge.

It was only a matter of time before the Death Eaters had enough evidence to condemn Esme and Regulus as traitors - and if the Dark Lord was ever defeated, there was nothing to stop any caught Death Eaters from dobbing in the two of them in exchange for mercy.

They had a narrow window for escape but also a lot of people they wanted to protect, so even if they could get to safety, Esme wasn't sure if she'd want to leave.