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 was shifted forwards and backwards to match up. One major BBC Sherlock character's gender was changed for the sake of the plot. Readers beware!


Chapter One: Pascal's Wager

Harry Potter imagined himself doing many different things when he returned to London, after spending a month in the country. Listening to an old couple talk for seemingly hours whilst trying not to slouch or sigh was not one of them.

"…which wasn't the way I'd put it at all, silly woman," the woman rambled. "Anyway, it was then that I first noticed it was missing. I said, 'Have you checked down the back of the sofa?' He's always losing things down the back of the sofa, aren't you, dear?

"'Fraid so," said the man.

Harry let out a tiny sigh and clawed at the armrests of his leather chair.

"Keys … small change … sweeties," the woman went on obliviously. "Especially his—"

"Glasses," the man and woman said, almost simultaneously.

"Blooming things," continued the woman. "I said, 'Why don't you get a chain, and wear 'em round your neck?' And he says, 'What, like –'"

"Larry Grayson," the couple said together.

"So did you find it?" asked Harry, his frustration getting the better of him, "Your – lottery ticket?"

"Well, yes, thank goodness. We caught the coach on time after all," said the woman matter-of-factly. "We managed to see, er, St. Paul's, the Tower …"

That moment, the door to the living room opened and a girl dressed for outdoor exercise and had her thick brown hair up in a high ponytail walked in. Harry stared at her in surprise.

"Sorry, you're busy," Julia Lestrade said as she glanced at the grey-haired couple.

Then she blinked as she took in the sight of a man who looked like Sherlock thirty years into the future, and a white-haired woman who had Sherlock's eyes and wore a black jacket with the collar propped up.

"A friend of yours, dear?" asked the woman as she studied Julia with considerable interest.

Harry quickly got to his feet. "It's time for you to go."

"Oh, is it?" said the woman.

"Yes," said Harry, as he gestured wildly at the wall clock and the door.

The couple got up from the couch obligingly. Julia jumped out of their way and stood by the table.

"Tell him to ring up more often, will you?" the man said as he took out a white, foldable cane.

"Umm … well …" Harry stuttered.

"She worries," said the man, his milky eyes downcast towards the woman's general direction.

Harry sighed. "Okay. Bye."

The woman briefly stroked Harry's cheek before she headed out, an arm hooked around the man's neighbouring elbow. Harry hastily shut the door behind them.

"Sorry about that," said Harry as he leaned against the door.

"No, no, I didn't knock, sorry," said Julia, wide-eyed. "So who were they?"

"They're…"

Harry paused. He didn't know what to call Mr. and Mrs. Holmes. 'Grandma and Grandpa' felt about as awkward as him calling Sherlock 'Dad'.

"…Sherlock's parents," he said eventually.

Julia blinked, "His parents."

Harry nodded. "They came with us to be in town for a few days."

"They are his parents," muttered Julia, now looking out by the window.

"Mycroft promised to take them to a matinee of Les Mis," sighed Harry, "he'll probably try to talk me into doing it."

Julia exhaled. "Well. That's …" she looked at Harry, then down the window and back again.

"What?" Harry asked, frowning.

"I mean, they're just … so…" stammered Julia.

Harry looked at her.

"…Ordinary," she finished.

Harry snickered. "Sherlock says that the cross he has to bear."

Then he went and resumed his seat on the leather armchair. Julia walked away from the window and sat on the red one.

"Looks like you've been running a lot," said Harry, noting the muddy running shoes on Julia's feet.

"Grandpa's been putting me through the paces," said Julia.

"Oh, yeah, how is he?"

"He takes me to Seattle for trail running and then spends the afternoon hiking the Shenandoah Mountains."

Harry squinted.

"Correct me if I'm wrong, but didn't he get shot a month ago?"

"Do you think a gunshot wound can stop him?" Julia huffed. "Mind, he's not a complete monster. He's under doctor's orders to not use magic until he completely heals and he's listening."

"How does he travel to Seattle, then? A broom?"

"Too far, and you can get shot down. Literally," said Julia. "Robert has a wardrobe that takes you to Mt. Rainer."

Harry smiled. "He would. Now what about Ron, Neville and Hermione? How are they doing?"

"Fudge tried to take Ron to court for what happened at the last task of the Triwizard Tournament," said Julia calmly. "But the Wizengamot threw out the case; said he had no grounds for a suit. He's out of the office now."

"Good," said Harry, feeling very vindictive. "What about Hermione?"

"Panicking over O.W.L.s. and the war."

"Of course. I assume Neville's getting harassed by his relatives over the same."

"He hid at my place and Ron's when it got too much," said Julia, lips twitching. "So what about you, did John and Sherlock stuff in you cage and abandon in you in a forest? Where are they, anyway?"

"Out. And nah, I just did a lot of running through grasslands and hills," said Harry, rolling his eyes. "Well, I say a lot … John cut my training in half when I went down with a cold after thirty minutes of running. What's up with alternative magic and running, anyway?"

"If you don't know, how can I know?"

"Your grandfather is the Grandmaster. You tell me," Harry retorted.

"Geezers like grandpa rarely explain; they just tell you what to do and expect you to obey," parried Julia. Then she paused. "Most of my training was endurance training, and it sounds like yours was, too. Since the magic requirement for Dao-ga is a lot higher than mainstream wizardry, I think that's why everyone's pushing you to run."

Harry nodded. Practitioners of Dao-ga— an obscure, dying branch of magic— didn't use wands, but cultivated their magic to the point it saturated their entire body, thus making their own body a wand, to cast spells. The reason why Harry had to learn it was if he could consciously control his magic, he would be able to transfer the soul fragment of Lord Voldemort currently residing in him to someone else if he gave his magic to that person. This was possible because life and magic were intrinsically tied together, so when one gave their life to someone else via blood donation, one gave their magic also.

While many preferred that he, Harry, would give the soul fragment to someone who was on death row or about to die from illness or old age, since the person's death would also mean the soul fragment's death, Harry instinctively knew it wouldn't work as neatly as they thought. For one thing, they would have to find a death row inmate about to get executed, was willing to house a soul fragment of Voldemort, and wouldn't spill the beans to a Death Eater — a tall order for anyone. Yet more importantly, the new receptacle of the soul fragment had to be human, magical and willing. The only person who met all requirements, and was willing to take something as vile as a fragment of Lord Voldemort's soul, was Dr. Robert Dongyi Ju, husband-to-be of Julia's maternal Aunt, Jacqueline Shin. Harry had been too desperate to refuse the most generous offer. So all Harry had to do was learn Dao-ga.

But therein lay the problem. In order to learn Dao-ga, one had to cultivate one's magic, and the only way to cultivate one's magic was to challenge one's life with hardship. Since one of the simplest and most straightforward forms of hardship was physical fitness training, Harry had decided to take that route. However, Harry's fitness level was such that he would find himself emptying the contents of his stomach after a mere thirty minutes of running and then lying in bed the next day with cold-like symptoms.

"Over-training," John declared when this happened for the first time. "We're going to have to dial down a bit…"

"I can keep going," Harry protested weakly.

John lightly bopped his head. "You won't. Not if you want to keep your body intact."

So John switched Harry's training to series of body-weight exercises, short runs (defined as twenty minutes) at maddeningly slow paces, and burpees. The latter usually left Harry flat on the ground, drenched in sweat, muscles aching and cursing the day he was born. It wasn't long before Harry started to notice a pattern. He was fast, but only in short bursts. That was no good, because for Dao-ga, stamina was everything. Yet try as he might, he didn't seemed to be lasting any longer. This pointed to an unbearable, but unescapable conclusion: the greatest weakness of the wizarding world was … Harry himself.

Harry looked down at his knees as the thought hit him hard once more. As usual, the pain was as crippling as the first time.

Julia, who watched Harry quiet down, spoke after a beat.

"You don't have to run to learn Dao-ga," she said carefully. "Grandpa's cultivated his magic through dancing."

That jolted Harry rudely. "That's a disturbing image," he muttered.

"Dancing is required for Baksu Mudang. Uncle Jeremy told me grandpa once joined a ballet troupe for—"

"Okay, stop!" Harry shouted as he covered his eyes. "I get it!"

Julia smirked briefly before sobering.

"Why not music? You're pretty good at the violin."

"Not that good," Harry protested.

"You're good enough to audition!" said Julia earnestly. "C'mon, what if—"

"I know, I know," Harry interrupted. "I'm actually going to ask Dumbledore what he thinks about me switching to music."

Julia let out a sigh of relief. "And if he's favourable, no more running?"

"I'll continue," said Harry, "Just not as intensely; hedging my bets and all that."

"That is safer, I suppose," said Julia. "So are you up for a run now?"

"Yeah, sure," said Harry. Then he raised an eyebrow at her. "John asked you to ask me, didn't she?"

"Why else would I come here?" said Julia teasingly before adding, "Seriously, though, I'd like a running buddy. I can't ask Hermione or Ginny 'cause they both think I'm nuts for running at all. I do okay alone, but it gets lonely after the first hour."

"'First hour'; ha," Harry muttered as he stood up. Then he smiled wryly as he recalled the talk that made him continue the much despised running…

-oo00oo-

About two weeks into summer holidays, Harry started hiding from John so as to avoid training, which he by then considered a brutal and futile exercise. Sherlock, of course, found him within ten minutes.

"What are you doing here?" he demanded the second time it happened. "Why aren't you training?"

Harry shrugged. Sherlock lifted an eyebrow at that.

"What's troubling you?" Sherlock asked in a low voice.

Harry shrugged again and then looked away. Soon he heard Sherlock exhaled through his nostrils.

"What – is – troubling – you?" Sherlock enunciated.

An awkward atmosphere descended in the room as Sherlock's question remained unanswered. It soon turned to toxic smog like consistency. Sherlock, of course, was entirely unfazed and bore his intense stare at Harry, silently demanding an answer. Harry stubbornly kept his mouth shut as long as he could, despite knowing it was useless.

At last Harry caved.

"I don't know what to do," he said helplessly.

Sherlock nodded knowingly.

"You have a habit letting your intuition guide your decision-making," he said. "That's only going to leave you paralyzed right now. Instead, think rationally."

"But how?" Harry cried.

"Use Pascal's Wager," Sherlock replied.

Harry frowned. "What's that?"

"The famous French mathematician Blaise Pascal defended his belief in God in the following manner," Sherlock explained. "Suppose God doesn't exist. The atheist wins, and the believer loses. If God does exist, the situation reverses. The consequences of being wrong with each belief, however, differ starkly.

"If God doesn't exist, all the devout believer has lost is the opportunity to fornicate, imbibe and skip many boring religious services. And since how you live doesn't matter at all in a godless universe, neither person has lost anything because there is nothing ultimate to lose to begin with. But if God does exist, the atheist roasts eternally in hell. The rational person— at least one who is convinced the Almighty cares about how we behave and what we think— thus chooses to believe God exists."

Harry nodded slowly. He could follow the argument, and the logic was clean. Yet he couldn't help but feel that there was something missing. He also couldn't connect the argument to decision-making, but rather thought it sounded like Sherlock agreed with Pascal.

"Note that I've said nothing whatsoever about my own conclusion on the matter," said Sherlock, a knowing smirk on his lips. "You should also note Pascal's Wager is not an argument for or against the existence of God. It's simply a practical application of statistics and probability."

Harry frowned again. Why was Sherlock bringing up statistics and probability? What did it have to do with his future?

"You have one pressing and unavoidable goal in your life at this moment, and that's defeating LV," Sherlock stated. "You may rationally believe that you will win. If you are certain of this, then preparing for a life beyond the final battle is the correct response to this assumption. But you cannot be sure. There exists the possibility that you may lose. So you must factor this when you decide on how to spend your time.

"If you split your efforts between preparing for the final battle and your life afterwards, and you are wrong and you lose, it won't matter because you will most likely be dead. But if you are right and you do win the war, all you've lost is the chance of having a more prestigious future.

"Now, suppose you spend all your time on battle preparation and you are wrong. Then you're still dead or as good as. But if you win, you are ruined because you've burned all your bridges. Again, suppose you go all in preparing for your future after the battle. This increases your chances of dying, which defeats the purpose of preparing for that future, but you would sit quite prettily indeed if you do survive."

Harry pulled a face. Of course Sherlock wouldn't consider how much he, Harry, would hate himself if he made such a selfish decision as the latter.

"So if you are wise, what would you do?" asked Sherlock.

"Do both?" said Harry, still grimacing.

"Yes," said Sherlock, nodding. "This gets into the heart of your dilemma. Your goal is not maximizing the chances of winning, but rather simultaneously increasing the odds of a good life after the war and minimizing your chances of dying. Now for you, a good life after the war is densely tied to how well you handle the battle, isn't it?"

Harry nodded curtly.

"So your instinct may tell you to pour all your efforts to battle preparation," Sherlock went on. "You'll be stupid if you do. Remember Pascal's wager: what will happen to me if my assumptions are wrong? Preparing for your future after the war is not nearly as costly as going all in on battle preparation."

"But I have to do it!" said Harry furiously.

"Of course," said Sherlock, raising an eyebrow. "You're going to hedge your bets and do both, aren't you? Now however you divvy up your efforts—and I recommend an 80/20 percent split, 80 going to the most important item—you need time. The only way you can have time is eliminating anything that is irrelevant to your goal. Your school work and classes are fixtures that take about 80% of your day, but since it covers prep for your future as well as battle prep, you can leave it as is. This leaves you about 20% of extracurricular time. It is here you can make changes. Take, for instance, Quidditch."

Harry felt his heart drop to his stomach.

"Y-you think I should quit?" he stammered.

Sherlock shrugged carelessly, "Unless you were planning to go professional."

Harry swallowed hard as he thought about it. Truth be told, he had fantasies of standing in the middle of a golden Quidditch pitch, wearing England's colours, while Ludo Bagman's magnified voice hollered: 'And I give you… Potter!' since watching the Quidditch World Cup last year. However, these fantasies were just that: fancies. He wasn't like Oliver Wood, his old Quidditch House Team Captain, who was now playing for Puddlemere United in their reserve team. Quidditch didn't define his entire life.

"…I should," Harry admitted painfully. "It's not like I can play for more than an hour…"

"So you gain an hour," said Sherlock, smiling in approval. "The next thing to consider is your music lessons."

Harry stared, startled. Both Sherlock and John had been so adamant about music lessons, it hadn't occurred to him Sherlock would actually allow him to quit. He also felt surprised when an intense feeling of regret, quite similar to the one he felt when he thought about quitting his House Quidditch Team, stabbed through his chest. He couldn't understand it; he dreamed of quitting violin. So why did he feel regret?

"Unlike Quidditch, your music lessons are more than just entertainment," said Sherlock. "Through it you have relations with Jacqueline. I was also told music is one of the three venues through which you can learn Dao-ga, which is directly related to battle prep."

Harry sagged. Of course Sherlock wouldn't let him just quit.

"I know you're training for long-distance running to learn Dao-ga," said Sherlock, giving Harry the Look. "You have the temperament of an athlete, so running makes sense. However, it would be foolish to simply discard violin when you've already built two years of experience. You also don't know which option will be more effective. Don't forget Pascal's wager."

Sherlock then bore his piercing eyes into Harry's.

"I'll leave the final decision to you," he said. "Choose wisely."

-oo00oo-

Final Notes: Mummy and Daddy Holmes are trying to get better at the business of small talk and pretending to be normal (ha). Harry knows the former (but not the latter), and is trying to honor their efforts ;)

Sorry for the lack of update. These past 2 weeks, I've been running around as though my head's been lopped off after receiving news that I might get laid off/made redundant. I'm using whatever time I have—which isn't a lot, unfortunately— to write this. I've got interview(s) lined, but who knows … I do hope for a good outcome ;)