This chapter ended up being so big that I've had to split it up! So as a result this story will be extended to 58 chapters as of right now (there may be more as I write and expand upon the Deathly Hallows part of this story) and next week's chapter will in reality be part 2 of this one.

I saw the incantation for Fiendfyre used here on a reddit post and absolutely loved it, so thank you u/viol8er for the inspiration!

I hope you all enjoy this chapter!

27/02/25: Reuploaded due to an error that made the chapter fail to load up.

It took three repetitions of Kreacher's tale for it to truly sink in for Sirius, as the elder man stumbled over to the nearest sofa and collapsed into it, his hand scratching at his beard awkwardly. "So Reg…" He muttered, the hang over evident in his voice as much as it was his eyes. "He actually turned on Voldemort? He died opposing him? He didn't just get scared and… flee?"

"No, Regulus was seemingly one of the bravest of his generation." Leo explained, never taking his eyes away from the locket throughout all of this discussion. It was a heavy item, golden with a large green S in the shape of a miniscule snake slithering across the face, and it brought about a strange feeling within Leo as he held it in his hand, a feeling that gave him a sense that he should be disgusted with it and throw it as far away as he possibly could, but at the same time he also wanted to pull it closer; to learn all of its secrets… He clenched his fist around it as he closed his eyes tightly, trying to regain control of himself by shaking his head fiercely. "He didn't run, he didn't flee like a coward. He was clever and brave in managing to work out the truth about the Horcrux and find a way to retrieve it without Voldemort knowing… and he is a big reason why we are now a step closer to defeating him."

Sirius swore under his breath as the revelation seemed to completely sober him up. He leant forwards and hung his head in his hands. "I never would have thought… I thought I knew him." His voice was muffled by his hands. "But all this time…"

"You'd left this place when he was 15." Leo explained. "Things change, look at what's happened to me since I turned 15…"

He had made a point that seemed to resonate greatly with Sirius as he sank deeper into his chair once more, nodding his head. "Bloody hell…" He whispered again, before his own eyes settled on Leo's clenched fist, the one holding locket. "So now what?"

"We destroy it." Leo said firmly, pulling his wand out of his jeans pocket with his spare hand. "If we can destroy it before Harry turns 17 then that's one less thing for him to worry about." He took a deep breath and looked towards Kreacher, who was still stood in the doorway looking on at them wide eyed. "Kreacher, can you put protections up so that the house is secure?"

Kreacher bowed his head slowly, but surprisingly less sarcastically than usual. "Yes Master." And the House Elf clicked his fingers.

A golden bubble began to spread from inside Leo's fist, warping its way around the room by pressing into every small bit of furniture like a protective wrapper. In his bones Leo knew that it was a powerful shield, one that seemed to hum around him. He turned to the Elf with a warm smile. "Thank you, Kreacher."

Kreacher bowed again, an action that was seemingly too much for the third person in the room as Sirius muttered from beside him. "This is so strange."

"Kreacher has been very helpful so far, we wouldn't have found this without him." Leo held his fist up towards Sirius as he turned back to his Father. "It's only fair that we help him now, help him to complete Uncle Regulus' final wishes."

Kreacher had a tear drop from his large, bloodshot eye and Leo nodded at him politely, before returning his focus to the locket, placing it down on the protected 19th century table. He took a few steps back before pointing his wand towards the Horcrux. "Confringo."

A blast of flames shot out of his wand striking the locket with a loud boom. The area erupted into flames leaving Leo to duck behind his arm to protect his eyes. Once a few seconds had passed and the flames began to dissipate he dropped his arm and hoped that it had worked, though the locket remained on the table looking as pristine as it had beforehand.

Sirius growled as he stood up from the sofa, his own wand in his hand pointed at the locket. "Bombarda." A loud boom followed and the locket shot upwards off the protected table, but as soon as it hit the golden barrier covering the ceiling it bounced back down and slammed down into the table again, unharmed.

"Reducto."

"Expulso."

Nothing they did was working, and Leo was starting to get extremely frustrated as each spell refused to even scratch the locket. "Sectumsempra." He muttered angrily as he jabbed his wand towards the locket, but once again the spell did nothing but annoy it as it started to hiss.

"Leave me alone for a moment." Sirius stated bluntly, his wand still trained on the locket. He saw that Leo was about to argue, but before the teenager had a chance Sirius snapped. "I'm about to try something and just on the off chance, I don't want you in here to get hurt." Leo stood still for a moment defiantly, not wanting to go anywhere until the locket was destroyed, but he lost the stare off between father and son and moved outside of the drawing room, slamming the door behind him angrily when a burst of bright green light illuminated the gap of the door. Leo paused for a moment recognising the Killing Curse immediately and feeling surprised that instead of horror or anger at the memory of the last time he had seen that spell, his first thought had been hoping that it had worked. "No." Sirius called through the door bitterly, and Leo opened the door to see that through Kreacher's protection a large scorch mark had appeared on the table, but the locket itself remained unharmed.

Leo kicked out at the nearby armchair, the protection engulfing it simply knocking his foot back without making any impact. "There must be something!" He exclaimed angrily, but he couldn't think of any more spells more destructive than those already cast, and in a huff, he grabbed the locket and stormed out of the room towards the library on the third floor hoping to find something that he had missed.

He was all out of luck, however, and after around 2 hours of searching through and then throwing around a dozen of the foulest books he had ever seen anywhere he could around the library, he curled up against one of the bookshelves and dropped his head between his knees, all of his prior joy at finding the locket and being able to do something to help was gone, and an overwhelming feeling of despair and disappointment had taken its place, eating away at the 17-year-old.

He finally poked his head up again at the sound of hurried footsteps racing up the stairs towards him, and the door burst open to reveal a frantic Sirius, his eyes wide and sober in a panic. "Get any essentials packed in a bag quickly and meet me downstairs."

"What's going on?" Leo asked.

"Snape's told the Death Eaters the secret. They're coming for the house." Sirius told him hurriedly, before bolting up the stairs to his own room to do his own packing.

Leo immediately sprang into action, racing to his room and quickly scribbling out a note to Ron telling him that Grimmauld Place was under attack before releasing Cosmo from his cage and tying it to the owls leg. "Take this to Ron." He told the owl, before casting a disillusionment charm on the bird and letting it out of the window, hoping that would be enough.

Then turning to where his trunk and backpack lay, he pointed his wand towards it, silently casting both the feather-light charm and the shrinking charm until the trunk was able to fit neatly inside his pocket. Finally he pulled his backpack over his shoulder and bolted for the door… only to rush back into the room and pick up the DA Galleon he had thrown earlier that day.

After magically sealing the door to the library in the hope that not even Snape would be able to enter, he met Sirius in the downstairs hallway as the elder of the pair was casting a number of strange wards, hexes and curses. "Ready." Leo called out, causing the man to stop his casting and look over to Leo.

"Is that all?" Sirius asked.

Leo nodded, tapping the strap of his backpack. "Extension charm."

"Good." Sirius nodded his approval. "Kreacher will meet us there, so don't worry about him." He finished his sentence by waving his wand to finish his casting, and took one look towards his mother's portrait curtain as a grin formed on his face. "I've always wanted to do this to this house." He pointed his wand at the curtains and they blasted open.

"FILTH! MUDBLOODS! BLOOD TRAITORS DEFILING MY FATHER'S HOUSE!" The portrait shrieked.

"Oh shut up you old bat!" Sirius roared back, before turning to Leo. "Outside, now. Wand ready."

"But the statute…"

"Isn't binding when in a life or death situation." Sirius explained impatiently. "And we're bloody well about to be in one if you hesitate! So move!"

Nodding, Leo rushed towards the door, jumping over the troll leg umbrella stand as he went and burst out of the door. Considering it was the height of summer the weather outside was damp and drizzly. That had been the norm for the summer so far though, but the biting cold and the rapidly settling mist indicated something more was on its way. Holding his wand ready, Leo looked in the direction that the mist was coming from and his whole body fell numb at the dozens of black specks that he could see in the distance soaring towards him. Grimacing, he focused on the memory of that day on the lake back in April, and the feeling of Hermione's lips on his own. Feeling warmer, he roared. "EXPECTO PATRONUM!"

A large, silvery Irish Wolfhound raced from the tip of his wand and did three laps around him before settling protectively in front of Leo as the Dementors grew closer. The door slamming on his right diverted his attention for a second as Sirius appeared beside him, the elder of the pair looking over at the oncoming creatures with an expression of sheer loathing. "That's the stuff." He growled, his grey eyes blazing black as he turned back to the house and muttered in a low, hateful growl. "Malignis."

Leo gasped and his patronus almost faltered as a result of the heightened distraction, because as he turned back to the house he saw the cursed fire he had only read about before spurting out from Sirius' wand like a hosepipe through the open doors of Number 12 Grimmauld Place. Despite the searing heat of the nearby flames a sense of cold crept back through Leo's body making him shiver slightly, and so he focused more on his happy memories by the lakeside and that kiss, with the Wolfhound seeming to grow slightly larger as the Dementor's were within range. Once they were three doors down a large pulse of silver energy sprouted from the dog, slamming into the Dementors and causing a shrill shrieking sound to echo down Grimmauld Place. The pulses continued as Leo poured everything he had into the spell, throwing the Dementors back as if they were caught in the middle of a tornado.

"Come on!" Sirius called out frantically. In the time taken for Leo to drive away the pack of Dementors Sirius had managed to set the entirety of Number 12 ablaze as thick flames were roaring hungrily, leaping out at the windows and causing them to shatter from the heat.

Leo was about to take it when he remembered the heavy item within his pocket, and as it often did, the voice of Hermione Granger filtered into his mind…

"To destroy a Horcrux, the object containing the soul fragment must be destroyed beyond all methods of repair."

"Beyond all methods of repair." He repeated, grinning as he pulled the locket out of his pocket, and in one swift movement threw it deep into the burning house.

The entire line of houses erupted in an ear splitting blast, lifting both Leo and Sirius high into the air and backwards into the road, with Leo landing with a heavy thud. Groaning as he regained his senses he looked around in horror at what he had done, watching as the entire row of houses along Grimmauld Place resembled a war zone more than a London street with debris raining down upon them from all of the houses. Inside Number 12 he saw the flames warp and twist with a pained, hissing scream that would haunt Leo until the day he died, but before he could react more and try to help the Muggles that were gathering he felt a hand grab his arm tightly, and with a crack, Leo disapparated.

By the time that it had registered in Leo's brain that they had Apparated, Sirius was already striding up a gravel path towards a modest two story house surrounded by tall trees, wand out and muttering protection charms. Leo made sure that his backpack was still on his shoulders before rising to his feet and following him.

"Where are we?" Leo asked impatiently, just one of around three dozen questions firing around his brain all at once. "Why… Fiendfyre?" He then levelled accusingly. "Why the bloody hell did you use Fiendfyre?"

Sirius scoffed derisively. "It worked, didn't it?" He then held his wand up. "Protego Maxima, Protego Horribilis, Salvia Hexia."

"But…" Leo stopped, the explosion still ringing in his ears. "All those people…"

Sirius stopped throwing protective spells up and turned to Leo, grabbing his neck tightly with each hand. "You did what you had to do to survive. Never apologise for that." He then pulled Leo in for a tight hug. "And you got rid of that thing, that's the most important part. Voldemort has one less Horcrux in the world now, thanks to you."

"You think it's really gone?" Leo asked, realising now that things had calmed down slightly that he had been extremely rash in just throwing it.

"It's gone." Sirius said darkly. "So is the house… nothing survives Fiendfyre."

Leo nodded, understanding all of that but now thinking solely of all of those people in the many houses in Grimmauld Place, hoping more than anything that he hadn't killed a bunch of Muggles. He was led inside the house by Sirius, noticing already that Kreacher was already in the kitchen rifling through the cupboards moaning at the state of the pots and pans. "Where are we?" Leo asked again as he looked around at the modest hallway.

"My place." Sirius explained, dropping into a wooden chair and taking a deep, needed breath. "When I turned 17 my Uncle Alphard died. He was another one that thought Pure Bloods were something special, but luckily for me, he cared more for family than he did his ideals. He argued when my Mother blasted me off the tapestry and left me a decent amount of gold when he died so that I wouldn't live a life beneath my station as a Black." Sirius drawled, the displeasure in his voice evident. "I used the gold to buy this place. James' parents lived nearby so it was ideal, I could visit whenever I wanted and Euphemia helped look after it in our last year of Hogwarts, bless her heart, she died not long after that..." He trailed off, lost in his memories for a moment before managing to snap back into the present. "Once we left school, your Mum and I used it as a…" He trailed off, but Leo understood completely, feeling the urge to shiver as he thought on exactly why his parents would need an empty house to meet up. "Anyway, when I got pardoned, it got returned to my possession, we were fixing it up last year together, your mum and I, in case we needed a place to escape to."

Leo dropped his backpack on the floor and moved further into the kitchen, admiring the basic wooden units that surrounded the room, and the cosy table in the centre. He was only stopped his exploring once Kreacher snapped his fingers and a pair of three tier sandwiches floated over to the table. "Thanks Kreacher." Leo muttered, realising just how hungry he was as he tucked into it.

He was still worrying about his actions at Grimmauld Place however, and Sirius could see that. Sirius looked around briefly before jabbing his wand wordlessly at the radio, with the audio device roaring into life as Leo recognised the Muggle news.

"…and finally news is just coming in to us of an explosion in Islington today. Officials at the scene of Grimmauld Place are reporting a major gas leak has caused an explosion that has decimated 9 houses along the road and has left 7 people hospitalised with burns and smoke inhalation, though thankfully there are currently no reported fatalities…"

Leo breathed a loud sigh of relief as he sank into his chair, his fear of his own actions evaporating instantly. "Nobody died…" He whispered to himself.

He noticed Sirius also looked brighter having listened to the newscast, turning it off as 'I wanna be the only one' was announced as the upcoming song. "We need to let people know we're ok." Sirius then began, not wanting to dwell on what Leo presumed was more guilt for having cast the dangerous spell. "Can you cast a voiced Patronus?" Leo shook his head. Sirius gestured for him to come closer. "Here, watch carefully.

It took less than ten minutes for Leo to be able to send his Wolfhound away to Hermione and Remus Lupin, while Sirius sent his own Patronus away to Bill Weasley and Harry explaining that they were safe. It was tempting, Leo thought, to include the fact that they'd rid themselves of a Horcrux, but Leo realised that that news was better off said in person where he knew that no prying ears could listen in. Once they had finished their messages and Sirius poured a glass of Firewhisky, something that Leo frowned at but relented when he decided that after the days ordeal he could really use one himself, he went to take his glass and his backpack upstairs to scope out the rest of the house, only stopping in the doorway at the nagging question that had sprung to mind since he had learned nobody had died. "How do you cast it?"

Sirius knew exactly what spell he meant, and grimaced at the thought. "It's dark, Leo. It's the opposite of a Patronus, you need to really feed into your hatred and destructive thoughts." He took another swig of the drink, staring at the bottle afterwards before shaking his head and capping it. "I have too many of those at the moment." He added bitterly.

Leo paused in the doorway not knowing how to react to that, but certainly feeling like he too had enough anger and hatred bubbling within him to be able to cast Fiendfyre then and there if he needed to. He tapped the door frame twice with his hands to signal his departure before walking away from his Dad and up the stairs, spotting that there were four doors as he reached the top floor.

In the first one he noticed what was clearly going to be his parents room. There were pictures dotted around the crimson walls of their time at Hogwarts, as well as what seemed to be a handful from after they graduated. Leo grinned at one in particular of his Mother, clearly pregnant with him at the time, pulling open a Christmas cracker with his Gran before he left the room, closing the door behind him. The next room was a large bathroom, while on the other side of the landing were two doors with small, golden plaques on the white wood. The right hand side plaque had Harry James Potter engraved, while it was the left hand side one that drew Leo's attention.

Leo David MacDonald

He pushed the door open and immediately tears began to well up once again, a regular occurrence since that night his Mum had been killed. The room was painted blood red, with silver and gold stripes falling down the walls intermittently, his Gryffindor and Wigtown loyalty proudly on show. There was a double bed in the centre of the room, and either side of the bed stood tall bookcases filled to the brim with various books, both for academic and leisure reading. Under the window was a writing desk, with empty containers ready to be filled with quills and other stationary, one thing that had seemingly been left until last. He tapped the wall with his hand when, on the windowsill, he noticed a picture. Moving closer, he gingerly picked the frame up, looking down as five pairs of eyes looked up at him. It was clearly a picture from the cottage by the sight of Lock Ryan in the background, and it was a summers day judging by the short sleeves and the clear skies. His eyes first spotted his Grandmother, her short white hair framing her face kindly as her eyes sparkled with joy. On the other side of the frame was Leo's Granda', clearly laughing his regular booming laugh.

It was the pair in between that caught Leo's attention most of all though. He recognised his mother instantly despite her clearly being younger in the photo… barely looking older than Leo was now. She was holding a child, clearly Leo judging by the hair and eye colour, and Leo guessed he was barely over 12 months old at the time that it was taken. She looked so happy, with her eyes constantly moving from baby Leo, to him, to the man on her left…

Sirius Black looked completely different, and it was only now that Leo realised exactly how much Azkaban had aged him. Gone were the hollowed cheeks and the age lines, and instead Sirius looked… well, Leo realised that he could see himself in the photo version of his Dad. Their hair was similar and the shape of their eyes… though Sirius had a carefree smile on his face there standing outside Leo's childhood home.

He didn't notice he was crying until his eyes became blurry from the tears, and so with a sniff he held the picture close to his chest, taking his trunk out of his pocket and placing it on the ground beside his backpack before he settled down onto the bed, holding the image of what seemed like a perfect afternoon close to his heart.

Reviews:

Lightningscar: Early, late, it's just always lovely to see an email saying you've reviewed! I had fun with the portraits, with the one in Leo's room being the Black ancestor that Anna of course bought the biography of as a present. That would have been quite funny, but I can also see Sirius not wanting to give the portraits the satisfaction even If they are muggle women! Sirius for sure isn't in a good place and he has more inner demons than most, which is largely why my created lore of Fiendfyre fits him so perfectly and why I had him destroy the house so effectively, because he is so angry and hate filled at the world right now that the spell is pretty easy for him to handle. The way I saw it with Kreacher was that he's very old and certain orders from people that he cared about more such as Regulus overrule blood, but Leo isn't as horrible to him as Sirius is anyway, and add in Hermione's influence and I just saw Leo being able to win Kreacher around and they'll always have some form of respect for one another now. Finding the locket, and now destroying it, will 100% have ramifications, though I'm hesitant to go into too much detail just yet.