A Study in Magic: The Application
by Books of Change

Warning/Notes: This is the sequel to A Study in Magic, which is a BBC Sherlock and Harry Potter crossover AU posted here. The HP timeline and BBC Sherlock's timeline were shifted forward and backward to match up. One major BBC Sherlock character's gender was changed for the sake of the plot. Readers beware!

Chapter Eight: The Marauders Meet

On the second weekend after the start of term, Remus Lupin travelled to Hogsmeade. He walked past the popular shops on the main road, entered a side street, and headed to a small pub that bore a swinging sign of a severed boar's head and the name "Hog's Head Inn."

Remus opened the rough wooden door and entered the pub. It comprised of one, dirty, and dingy room that has bay windows that are so encrusted with filth that you can barely see through them. The old man with a long grey beard behind the bar scowled at Remus, like his presence a deep inconvenience. Remus headed straight to the only patron present; he was notable in Muggle-ish attire: black leather jacket and dark jeans, and a white shirt.

"You're late," Sirius Black accused when Remus sat down.

"You're early," Remus replied. "You know how crazy a teacher's schedule gets?"

Sirius snorted. "You tell me. It always seemed like the teachers had enough time to take all the fun out of student lives."

He then waved at the half-full bottle of Firewhiskey on the table. Remus, after considering the dirty rag the old barkeep was using to wipe his glasses, opted to conjure his own tumbler.

"So what have you been up to?" asked Remus, once Sirius poured him a glass.

"Whatever His Highness Holmes wants, what else?" grunted Sirius, before adding in a low undertone, "Muffliato."

Remus took a sip of Firewhiskey while the muffling charm took hold of their surroundings. "So what is he up to?"

"Voldemort research," Sirius replied. "Like always. The funny thing is, I actually understand his reasoning."

"How so?"

"He's tracing his activities backward, from most recent to older. That makes sense; the further back in time you go, the murkier things get, and the amount of available evidence grows tinier."

"Yes, but how does the logistics work?" asked Remus. "Lord Voldemort and his Death Eaters have been spotted all over the world just these past two months. Is he sending you to every suspected Death Eater appearance?"

"Not recently. Before you ask, no, he didn't order me to join Hagrid and his mission to talk to the Giants. He also sniffed at Dumbledore's idea to offer the werewolf cure for free to the werewolf community. Interesting, but irrelevant, said he."

Remus shook his head. "Diagon Alley?"

"Himself checked it in person and decided there's no relevant data. Merlin alone knows how he managed without magic or getting caught."

"I'm not sure if I want to know," Remus remarked.

"You probably don't," Sirius agreed. "Yesterday he went to Little Hangleton."

"The place LV had been in hiding until his resurrection?" said Remus, eyebrows raised.

Sirius nodded. "Just the place."

"What was he expecting to find there?"

"Quite a lot, it turns out," said Sirius grimly. "Listen carefully. This is for your ears only."

Then Sirius launched into a detailed rundown of Sherlock's latest activities…


Little Hangleton was a sleepy Muggle village nestled between two steep hills, its church and graveyard clearly visible even from a distance. Across the valley on the opposite hillside, was a handsome manor house surrounded by a wide expanse of velvety green lawn. Once a fine-looking manor, and easily the largest and grandest building for miles around, the Riddle House was now damp, derelict, and unoccupied.

There was no apparent reason to believe the manor had anything of import, and yet Sherlock decided he needed to take a personal look all the same.

John came with them, little Benedict in his favourite sling. As he prepared to Apparate the three to Little Hangleton, Sirius noted since Harry left for Hogwarts, Sherlock and John were practically joint at the hip. Where one was, you would find the other also.

Sherlock entered the house through a back door. John was close at his heels, and Sirius brought up the rear. Sherlock roamed through every room, clearly looking for something and yet not taking out his magnifying glass for a closer look, as was his usual custom.

Then he stopped at once was the master bedroom. Sirius noted the unusual degree of dampness and heat permeating through the open door, not to mention the smell of putrefaction. Sherlock peered inside without entering. His piercing eyes roamed over the fireplace, the damp and molding wood floors, and the rotting high-backed armchair.

At last Sherlock entered. He took out a pocket knife and sunk the blade into a wall. It went right through like soft butter. John handed Benedict over to Sirius and joined his side.

"Human remains were burned here," declared John, after a few lungfuls of air.

"How do you know?" Sirius asked.

John's tongue darted out. "I can smell burnt blood, and the air tastes like rancid fat."

Sirius was about to ask John how she knew the taste of rancid human fat, but then remembered John had gone to several war zones before meeting Sherlock. Speaking whom which, the man was crouching next to a pile of white plaster.

No, not plaster. It was shed snake skin.

"What the hell?" muttered Sirius.

Sherlock didn't quip or sneer but took out his Muggle smartphone (it lacked flames during use) and started thumb-typing. Sherlock smirked at whatever he was seeing before re-pocketing it.

"What do you notice about this room?"

"Damp. Hot. Like a sauna," Sirius replied. Best get the obvious out of the way.

Sherlock nodded. "Appropriate temperature for a tropical snake. This skin," he waved at it, "belongs to a Burmese python. Note the distinctive pattern. Last year the London Zoo reported a female Burmese python escaped from its glass habitat. It was never found."

Sirius raised his eyebrow. "Are you saying Voldemort stole the snake? Why?"

"One of Snape's earliest reports said LV used a concoction of snake venom and unicorn blood to create a rudimentary body," said Sherlock. "He later reported LV is unusually attached to his pet snake, and that he went through great pains to place powerful protections around it.

"Burmese pythons are not venomous, so they are useless as far as collecting snake venom is concerned. And once he obtained a body, LV has no need for a snake. LV doesn't form attachments, certainly not frivolous ones, and cherishing a pet for sentimental reasons alone is too mundane for the likes of him. The Burmese python has a utilitarian purpose then, one that requires maximum protection."

Sirius and John nodded in agreement.

"Frank Bryce," Sherlock continued. "Late gardener of this most charming estate, murdered by the killing curse, almost a year prior to LV's resurrection. Magical Law Enforcement claimed his body the moment wizard involvement was suspected. Two months prior, Lestrade reported his body went missing. Now, why would a magical steal his body? He was a Muggle. He has no magical relatives and his blood has no magical value. It's already on record that Avada Kedavra was used against him. LV also had successfully resurrected himself by then. So why bother?"

"Maybe Voldemort added him to his Inferi army?" Sirius guessed.

Sherlock gave him a withering Look. "If he wanted to use his dead body to make it do his will, why bother going through the trouble of stealing it from the Ministry of Magic? He can kill whoever he wants. He can even murder one of his own demonstratively useless followers to make a statement."

If Sirius was a better man, he would've cringed at this callous statement like John.

Sirius was not a better man; he viciously wished Voldemort had done exactly that to Peter Pettigrew.

"What does LV want?" Sherlock went on. "Immortality. The ritual that allows him to be immortal, or at least the illusion of being immortal, needs a receptacle and a sacrifice. Murder is a key component. Frank Bryce was likely murdered by LV's own hand. Or wand, as if you want to be specific. The receptacle can be anything, according to Dumbledore. It can be a living thing, then, as inadvisable as it may be.

"There are several months between the snake theft from the London Zoo and Snape witnessing LV placing magical protection around what is likely the same snake. Meaning, LV didn't see the need to put those protections until later. The first day Snape reported to LV, he told him the diary that once held a piece of his soul was destroyed. Therefore he knows he's missing one of his Horcruxes. What explains the pet snake, the protection around the snake and the date it happened, the use of Frank Bryce's body, and LV's ultimate goal?"

Sirius didn't want to say it. He didn't even want to think it. So John did the honours.

"He turned his pet snake into a Horcrux."


Remus went quiet after Sirius finished speaking. As Remus imagined the sheer difficulty of killing off Lord Voldemort's pet snake, heart sinking like lead, Sirius drained his tumbler in several large gulps. He's been drinking a lot lately, Remus thought in passing.

"…Does Harry know?" Remus asked at last.

"Remember the secure wiki thing John suggested and talked Jacqueline into making? Sherlock posted a note there," Sirius said, after wiping his mouth.

Remus winced. He was of two minds about the secure wiki site. On the one hand, it allowed everyone in the Circle of Trusted Few to share important news concerning the Horcrux hunt using Muggle Technology, something Lord Voldemort wouldn't put much thought into. On the other hand, the wiki painted the most terrifying and bleak picture. Remus wasn't sure how Harry was able to sleep at night after reading them.

"That's enough from me," said Sirius after pouring another two fingers of Firewhiskey into his tumbler. "How is Hogwarts? How is Harry doing? What has he been up to? Tell me everything."

Remus dutifully rattled off Harry's latest antics and his own work as it related to them. Harry was going to all his classes and handling his prefect duties well. He took care of the first years like an older brother would, as he always had. Oh, he recently did something quite ingenious and kind. He put up these little maps in all the major corridors that pointed out where you were in the castle and gave you directions if you asked. The last bit made Sirius smile.

"That's a brilliant piece of charm work. What else?"

"He visits me in the evenings," said Remus. "For privacy and to have someone to bemoan prefect duties over."

"And talk to Mum and Dad," Sirius added with a twisted smile.

"There's that," Remus admitted because it was true. Harry's main reason for visiting Remus's office in the evenings was talking to John and Sherlock (and say "hi" to Benedict). These were by no means sentimental or warm. In the last meeting, John advised Harry if he lost his wand in a fight, he should either attack his opponent's knee or shove their nose bones into their skulls with the heel of his palm. Harry practiced both moves on a dummy, while Remus cringed in his corner. The bone-chilling reasons behind John and Sherlock's training sessions for Harry were not what put the downward twist on Sirius' mouth, however.

"He asks about you, you know."

Sirius looked down. "You don't have to lie to me."

"No, really, he does," Remus insisted. "I have a letter from him to you. Here, let me give it to you."

He took out the parchment envelope in his pocket and placed it on the tabletop. Sirius stared at it for several long blinks, before slowly sliding it towards him. He didn't open it.

"How are the night classes? Dumbledore mentioned he talked Shin June Hu into leading," Sirius asked.

"I'm not involved in them," said Remus, and thank Merlin for that. Even with the reduced number of students, due to several parents pulling out their children after the Ministry of Magic publically acknowledged Lord Voldemort's return, he was exhausted by the end of his work hours. "I've seen Grandmaster Shin only once, but I have seen Slughorn plenty of times."

Sirius' eyebrows shot up. "Slughorn? You mean, Horace Slughorn?"

"Yes, that Slughorn," said Remus with a smile. "Dumbledore convinced him to come out of retirement."

"Merlin's pants, how?"

"Beats me. Blackmail and bribery, maybe? He lost no time making himself back at home, though. He has his own office, he lounges in the staff room, and joins us at the teacher's table in the mornings."

"Is he revamping his Slug Club?" said Sirius shrewdly.

"Oh, yes," said Remus, lips quirking. "He already reserved a classroom for a private dinner two weeks hence. He's also been asking me about Harry. Last night he 'accidently' stopped by when Harry was at my office."

Sirius scooched closer, his tumbler forgotten. "Okay, now you really have to tell me everything. What happened?"

Remus grinned at his old friend and started to tell the story…


Remus learned Horace Slughorn had returned to Hogwarts when he saw him inside the staff room the day before the start of term meeting.

"Remus Lupin! Splendid to see you again, my dear boy!" Slughorn boomed from the armchair he barely squashed his enormously fat body into.

Remus remembered to close his mouth sometime after. "Hello, Professor Slughorn. I didn't expect you here."

"I didn't expect myself back here either, in my old age," said Slughorn, shaking his bald head. "I must be mad, yet here we are."

"You're here to teach?"

"Of course! But not kiddies this time. No, I'm teaching night classes for late-bloomers. Special favour for Shin June Hu, who's heading the whole thing. Said he isn't confident enough in potions to teach it." Slughorn looked particularly chuffed about the last bit.

"Now I heard you took over the Defence Against the Dark Arts position," said Slughorn keenly.

Here it comes, Remus thought. "Yes."

"First person to stay on longer than a year for the last sixty years, I was told."

"Yes, sir, though I'm as at lost as to how as everyone."

Slughorn wagged a stubby finger at Remus. "Come, you're not giving yourself enough credit. You were quite able as a student, I remember. Speaking of which, have you been talking to your old friends' son, Harry Potter?"

Oh, yeah, here it is, Remus thought as he collected himself. "Yes."

"Excellent. Tell me, what is he like? I'm hearing all sorts of crazy rumors about him and I don't know what to believe."

It was very easy to brag about Harry without revealing too much. Remus told Slughorn Harry had Lily's deft hand in charms and her kindness, and that he'd inherited James' transfiguration and Quidditch talent.

"I'd love to see him in person," said Slughorn with genuine feeling. "Perhaps I could swap a fifth-year potions class with Snape? Anyway, glad to hear his Muggle upbringing didn't do much damage."

"I credit Harry's Muggle parents for fostering his talent," Remus couldn't help but say.

"Aha!" Slughorn cried. "You too! Almost everyone here seems to think his Muggle guardians had a hand in his brilliance, particularly his foster father. What's his name…"

"Sherlock Holmes."

"Yes, Holmes," said Slughorn, a challenging gleam now in his eye. "Well, Lupin, you know I don't abide by the pure-blood agenda You-Know-Who touts. But it's one thing to acknowledge a Muggle-born can be as good as a Pure-blood, and another thing entirely to think Muggles can understand Magic. So how can a Muggle help a wizard? That's what I want to know."

Remus really should've known the wily old head of Slytherin would trick him like this.

"It's difficult to explain the inexplicable," he eventually replied, knowing full well he was being cryptic. "But I can tell you Sherlock Holmes is an extraordinary man, and Harry learned a lot from him."

Slughorn sagged into his seat, obviously disappointed. "I guess I'll have to see it for myself, then."

Slughorn did as he promised. The evening Harry came with his letter for Sirius, Slughorn knocked on Remus' office door and invited himself in. Slughorn's watery eyes flew to Harry's forehead and the lightning-shaped scar it bore.

"Well, quite different from my day," said Slughorn, now looking around Remus' office.

"Good evening, Professor Slughorn," said Remus, after a flustered beat. "This is Harry Potter. Harry, this is Professor Slughorn, my old potions professor."

"Hello," said Harry guardedly.

Remus offered Slughorn a chair and tea, for the lack of better ideas. Slughorn sat down and immediately his large round eyes slid over Harry's scar, this time taking in the rest of Harry's face, his shock of white hair and the prefect badge pinned to his robes.

"You look far more like your mother than I was told to expect," Slughorn remarked.

Harry tilted his head a little.

"You certainly have her eyes."

"So I've been told," Harry said.

"Hmpf. Yes, well. You shouldn't have favourites as a teacher, of course, but she was one of mine. Your mother," Slughorn added, in answer to Harry's questioning look. "Lily Evans. One of the brightest I ever taught. Vivacious, you know. Charming girl. I used to tell her she ought to have been in my House. Very cheeky answers I used to get back too."

Harry nodded his head slowly.

"So you were brought up by Muggles, just like her?" Slughorn asked.

"Yes," Harry replied.

"And your Muggle guardian is some sort of genius. Can tell your whole life story from a glance, or so McGonagall said. I can't bring myself to believe a Muggle can do that without magic."

Harry's expression turned cold at this challenge. Then he flicked his eyes up and down Slughorn. It was eerie how Sherlock-like it was.

"You're close the owner of Honeydukes, who believes he owes you a great debt," Harry began.

The look on Slughorn's face transformed into that of astonishment. "How on earth…?"

"You were the Head of Slytherin before Sna… Professor Snape," Harry went on. "Unlike most of the wizarding world, you believed the LV rebirth broadcast was real and went into hiding. Mostly in Muggle neighborhoods, and never in the same house for long. You are a Magical Mobile Network customer, but you don't trust Zing and its delivery service. Also…"

Harry paused for a second, like he was considering what he should say next.

"...You're very fond of crystallized pineapple," he finished.

Slughorn gaped at Harry for a long time. Remus was strongly reminded of a fat walrus yawning. Then Slughorn burst into hearty laughter.

"The cheek! Lupin, you told him about me, didn't you?"

Remus shook his head, which of course made Slughorn even more astonished.

"Then how did you figure all that out? Because you were absolutely right on everything!"

"Professor Lupin said you taught him potions," Harry explained. "That's a major subject. Professor McGonagall, Professor Flitwick and Professor Sprout's been the head of their Houses since Professor Lupin's time. You addressed Professor McGonagall without her title, and in the mornings, you talk to Professor Dumbledore like an age peer. You've been teaching as long as Professor Dumbledore, then. Considering the subject you taught and how long you've been teaching, chances are high you were the head of Slytherin before Professor Snape."

Slughorn slapped his knee. "I see! How absurdly simple! But I suppose everything is simple after you explain it. Now, how'd you know I've been in hiding? And that bit about Ambrosius Flume, of Honeydukes — a hamper every birthday, and all because I was able to give him an introduction to Ciceron Harkiss, who gave him his first job! How'd you figure that out?"

Harry quirked his lips up a little. "You received an owl delivery from Honeydukes."

"Yes. And…?"

"Honeydukes doesn't deliver, except through Zing. That they went through the trouble of sending you a bundle through Owl Post means that you know someone there who believes they owe you. That it was the owner was a shot in the dark, but a good one."

Slughorn nodded in agreement.

"Setting up a Zing account is easy, especially when you're a Magical Mobile Network customer," Harry went on. "And since the Ministry botched up the MMN, practically everyone transitioned to Zing. But not you. Why not? If you think about it, MMN is about as secure as the Floo Network, which is to say, the very thing that makes it easy to connect you to other people makes it bad at blocking others out."

"My thoughts exactly," said Slughorn. "But do go on."

"You're not teaching any day classes in Hogwarts, so you must be teaching the night classes. That Dumbledore thought about you at the same time as Grandmaster Shin means you must be a very talented wizard—" Slughorn puffed up at this "—and I don't think someone like you would've failed to notice MMN's security risks or take the Ministry of Magic's first take on the broadcast."

"Just so!" Slughorn confirmed with obvious pride. "A prudent wizard takes the whole body of evidence and makes up his own mind. He keeps his head down, too, in times like these. It's fine for Dumbledore to talk about making a stance, but that's tantamount to making you make yourself a target."

"Yet here you are," said Harry sardonically. "You must've realized the safest place to be if you're not a Death Eater or a Voldemort Affiliate is where Dumbledore and Mr Shin are."

Slughorn gave a shudder and a squawk of protest at Harry speaking Lord Voldemort's name out loud.

"Hmpf, well there's that," grunted Slughorn, after recovering. "After that dreadful broadcast, until Dumbledore and Shin got in touch with me, I've been on the move. And yes, from Muggle house to Muggle house. It's quite easy once you know how. One simple Freezing Charm on these absurd burglar alarms they use instead of Sneakoscopes and make sure the neighbors don't spot you bringing in the piano. But how'd you figure I opted for Muggle houses? Another guess?"

"If you were in touch with the Wizarding World since the resurrection broadcast, you would've at least heard about the Zing switch over. But on the first day of classes, though you had an MMN phone, you looked like you never heard of Zing Delivery, let alone seen it in person. So, you must've gone somewhere where you couldn't hear the latest Wizarding news without some effort and you must've left your phone behind for security reasons. I don't think you'd live rough, so that leaves Muggle neighborhoods."

Slughorn looked absolutely spellbound. "And the crystallized pineapple?"

"What does a man do when he returns home after a long time away? Indulge in his favourite foods. Your hamper from Honeydukes was eighty percent crystallized pineapple."

Slughorn burst out laughing. "Most excellent reasoning! By Jove, I've never met someone who thinks like you!"

"My Muggle dad taught me how to think," Harry reminded Slughorn. "No magic necessary. Just observation and deduction."

"Of course, of course," said Slughorn indulgently. "I definitely want to hear more of your unique way of thinking. Here, allow me to invite you to a little get together I'm hosting in a fortnight. I'll be inviting some of your classmates, as well. Good food, good company, should make for a wonderful evening. How about it?"

Harry did a closed-mouth smile that had just enough crinkle around the eyes to make it look sincere; something Remus had seen John do when Mycroft Holmes was around.

"Thank you. I'll try to make it."


"Didn't think Harry would let Slughorn collect him. He didn't notice?" said Sirius, after Remus finished speaking.

"I don't think he was particularly impressed by Slughorn or was interested in his dinner party," Remus replied. "But he did notice Dumbledore was bringing all people who would've known LV to Hogwarts. Slughorn taught him when he was a student, you know."

Sirius's eyes flew wide open. "You're right. Merlin, you never think Voldemort as a child, but he was once. Damn." He shook his head. "I knew Harry was good, but I keep getting surprised at just how good."

"And getting better every day," said Remus proudly.

There was a beat.

"So are you going to read your letter?" Remus asked.

"You just want to read it, too," Sirius scoffed. Nevertheless, he ripped the envelope open and spread the letter out on the table so both of them could read:

Dear Sirius,

I hope you're doing well. I'm writing because I didn't know how else to reach you. I didn't want to risk calling you or using the two-way mirror when you could be in the middle of a deep cover mission.

("So thoughtful," said Remus, to which Sirius retorted, a bit teary-eyed, "Shut up.")

I'm doing fine. Being a prefect isn't as bad as I thought it would be, but it's still more trouble than it's worth. I haven't had any meetings with Dumbledore yet, but Sherlock set me to research LV's earlier years since I'm in Hogwarts (back to interviewing ghosts again!). Basically, he's going backward and I'm going forward. I wonder what we'll find at the midpoint.

Speaking of ghosts… I've been working with this girl to talk to the ghosts from other houses. We usually hang out in a group, so everyone knows we're friends, but all of a sudden everyone's asking if we're dating. It's stupid, and I don't know what to think. I do like her, but I never thought about dating anyone. What should I do?


There was another bout of quiet while Remus and Sirius stared at each other with their jaws flapping somewhere around their knees.

"…Did Harry just ask me for advice about girls?" Sirius gasped.

"Seems so," said Remus, equally astounded.

"Why ask me?"

"Who else would he ask? Sherlock? Between the two of us, clearly I'm the person all the girls wanted growing up. Not."

"You're turning cynical in your old age, Moony," Sirius shot back. Then he drew a deep breath, "I don't suppose you know which the girl he's talking about."

"I didn't even know there was a girl until just now."

Sirius nodded slowly.

"Who could it be?"

Final Notes: I hope you enjoyed this update! I've posted more detailed notes on my blog. There I muse over what species of snake is Nagini and think way too hard about the secure wiki the Baker Street Trio may use to brain-and-info share.

Merry Christmas! From BOC
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