Hello readers! This was requested by Hyrule_And_Beyond. I hope you like it! (Also, people, am neither British nor Sheldon Cooper, so my knowledge of British trains is extremely limited. Please bear with me if some of the things I described aren't accurate)

Mycroft didn't know if he was going to make it. His palms were clammy, blood was pumping loudly in his head, infernal noise surrounded him, screams echoed everywhere and shrill sounds reverberated inside his mind.

He was in hell on earth.

He was in a train station.

Not that Mycroft held a particular grudge against trains, no. It's just that train stations contained so many people, so many awfully emotional people, blatantly disclosing possible weaknesses to enemies as they bade tearful goodbyes to those they clearly marked to watchful eyes as their loved ones. And most of all they were so bloody loud.

Nevertheless, ignoring the migraine that was beginning to form, Mycroft trudged on. He boarded the train to York and sat himself, with a heavy sigh and a disgusted look around, in the third class carriage.

It had been years since he had last taken the train, and it had never ever  been third class. He had grown used to what he called a certain level of comfort (but a more accurate word would be opulence), travelling in private jets and having chauffeurs drive him around. He was definitely not thrilled to be downgrading so brutally. But, begrudgingly, Mycroft settled into his seat, as his level of personal comfort was slightly less important than the fate of the modern world. Slightly. His posh habits would have to be thrown aside until he had the files.

Everything had been minutely planned so that not one hostile nation could predict who would be handing Mycroft the precious documents. As a result, not even he  would know until the USB key was slipped into his hand once arrived at the station, whence he would be promptly escorted by several MI5 agents to the heavily secured private jet in which he would return to London. To make the exchange as inconspicuous as possible, it had to take place in the most crowded part of the train, where everyone would be rising to get luggage and causing a great brouhaha once the train arrived at its destination. Unforthunately, that was third class, and unfortunately, Mycroft was the only official trusted with receiving the files, which explained why he was sitting in this crowded, hot, and awfully loud carriage.

Mycroft had at least made a plan to avoid death by boredom and overwhelming presence of goldfish. He placed his earbuds into his ears and started his music, drowning out the surrounding aggravating noises with the soothing notes of his classical music playlist. He then took from his jacket pocket the photos and notes from Sherlock's most recent unsolved case, determined to figure it out in order to gloat about it to his little brother. He closed his eyes and placed his fingers to his temples to think just as the train started moving, when he suddenly felt a presence nearby. Exasperatedly, he opened his eyes, only to nearly have a heart attack as a colourful explosion setting its bags down right in front of him practically caused him to go blind.

You had been looking everywhere for a seat. Everywhere. But, unfortunately, every person you had crossed had seemed to scoot over to take up more room or to set a bag down on the neighbouring seat upon taking one glance at you. People seemed to think that you dressed somewhat extravagantly, but that was because they were all pretty much wearing variations of the colour beige. But you just really liked fun and flashy colours, and honestly didn't care what other people thought of your fashion choices. The more radiant you were in colour, well, the more you were radiant in personality. Your current outfit was witness to this.

You were sporting all the colours of the rainbow, simply because you couldn't decide which was your favourite. But most of all, you were wearing a dazzling smile which was truly the cause for Mycroft's sudden need for sunglasses.

(Ok guys, I tried to draw something like the colourful outfit I had in mind, even though I realize it's not THAT flashy. Also, I spent 45 minutes and a lot of thought and effort on this, so please don't make fun of it)

(Anyway, on with the story)

Suddenly, you felt a glare weighing down on you and raised your head to see the man you were about to sit next to.

"Oh hello!" you exclaimed brightly. "Excuse me, do you mind?" you asked, gesturing at the free space next to him. "Everywhere else is full."

Mycroft glanced around, noticing that most of the seats were indeed full, if only occupied by bags and the like. He smiled his most pinched and fake smile to you, hoping to intimidate you into leaving. You, however, only looked at him, unimpressed.

Mycroft sighed. This was very tedious. He absolutely did not want this bubbly person next to him, who would most likely try to engage in conversation, a dreadful thought. Also, you could potentially compromise the transmission of documents. He decided to play on that.

"If you take this seat," he started, "I cannot vouch for your safety," he said in his most threatening tone, the one that reduced the most powerful men in the world to cowering puppies. Your reaction, however, both astounded and exasperated him.

"How very dramatic," you responded, with a not so slight hint of sarcasm. You were sick and tired of standing up, and you didn't care that this man so obviously did not want you to sit there. "But if you must know," you smirked, "I like to live dangerously." And with that, you plopped down into the (you had decided) available seat, not standing for any further objections.

Mycroft rolled his eyes and turned away from you, his earbuds plugged in, hoping to dissuade you from further conversation. This was going to be a long train ride.

***SOME MINUTES LATER IN TIME AND SPACE***

Tap tap tap tap.

Tap tap tap tap tap tap.

Tap tap.

Mycroft opened his eyes. What was that mysterious tapping noise? It was infernal, and he couldn't focus on Sherlock's case, which was already troublesome enough. He looked down, and saw your fingers drumming a beat against a book you had taken out. Of course.

Mycroft cleared his throat to attract your attention. He was spectacularly ignored.

Annoyed, he persisted in trying to indirectly attract your attention, not deigning to speak to you. Unfortunately, the only attention he was getting was from the people across the aisle, who were curiously glancing at Mycroft who was steadily starting to sound like he had a dying whale in his throat.

Finally, he spoke up because he couldn't stand it anymore. "Will you please stop that?" he asked, trying to sound not at all bothered, when he was internally screaming in anguish.

You smiled at him and stopped, seeing as you didn't want to wage war against him for the rest of the train ride.

"Sorry," you explained, hoping that maybe starting a conversation could settle the peace between the two of you. "Only, I couldn't help but notice you were listening to Le Nozze Di Figaro  and it's one of my favourite operas, so I got a bit carried away, tapping along to it."

The man glanced down at his phone and noticed that he was, in fact, listening to the overture of the opera. But he hadn't realized his music was playing loud enough for you to hear.

"How could you possibly hear-"

"Oh, I didn't!" you gushed. "No, don't worry, your music wasn't too loud or anything. I just know it so well that I didn't need to hear it to tap along."

The man didn't say anything, but he did look at you differently. He raised an eyebrow, showing that he was intrigued, maybe impressed. You smiled and extended your hand.

"I'm Y/N," you said.

The man hesitated, before taking your hand and giving it a shake. "Mike," he introduced himself.

Mycroft had  settled on a fake name, not intent on compromising the mission by giving his identity away. Mike had seemed the obvious choice of name, although he was cringing internally at having to use it. He hated how ordinary it was. But he thought it might be worth a go to talk to you, seeing as you seemed to have knowledge in something he was interested in, and thus shouldn't prove to be a complete drudge.

He surprised himself. He usually hated small talk and other people in general. But, you were so different from the drab, boring, lying, sucking up people he had to deal with everyday. It was refreshing. For the first time in a very long time, he sought the company of someone else, and that someone just happened to be you.

"Well, Mike," you said. "I would like to thank you for letting me sit here, even if it was reluctantly," you smiled, showing there was no harm done. "I think that most people are a bit put off by the fact that Luna Lovegood is my fashion icon."

"I must confess that I have no idea who that is."

"...whAT?" you exclaimed, absolutely flabberghasted. "What do you mean you don't know who that is? Luna Lovegood is such an amazing Harry Potter character and a role-"

"I haven't read Harry Potter. Aren't those children's stories?" Mycroft asked nonchantly.

You sputtered indignantly. For a while, you had no words. When you finally regained use of your voice, you launched into a spiel about the novels you loved. "Children's stories? Children's stories?  Harry Potter is not a children's story! It is a beautiful story that all can appreciate, whether young OR old! It talks about war, loss, sadness, the importance of family ties, friendship, love," at this Mycroft scoffed, "the need to stand up for what is right, sacrifice, and it's just so amazing! If it sold so well, it's because it could touch everyone. Even that guy in your picture liked it! And look, see this?" you raised your book to show him the cover. "This is Harry Potter and the Cursed Child, and it's absolutely-"

"What did you say?"

"What?" you asked, thrown off your groove.

"What did you just say, about the picture?" Mycroft repeated, a serious expression on his face.

"I said that the man, the one in this picture, he liked Harry Potter," you reached over to the printed image in question, which had been peeking out of Mycroft's file about Sherlock's case. You looked at the picture closely, completely unfazed by the fact that it depicted a gruesomely murdered man. Mycroft raised an eyebrow at your calm, but said nothing.

"Look," you said, pointing at the man's wrist. "Right there. A triangle, containing a circle and a line. That's the Deathly Hallows symbol. It comes from Harry Potter, and represents the elements that would make one the Master of Death," you explained. "Wasn't much use to him, though," you added, frowning at the victim's mangled body.

But then you noticed something. "Hang on," you said, bringing the image right up close to your face. Your eyes widened. "How long after the death was this picture taken?"

Mycroft took the picture out of your hands. "Unfortunately, as much as this proves your point about  Harry Potter," he said. "I can't allow you to look at it any longer, seeing as you should not have seen it in the first place. It is confidential crime scene information-"

"Then why do you have it?"

"-that civilians should not have access to as it would compromise the investigation," Mycroft completed, ignoring your outburst.

"But you have to listen to me!" you said forcefully.

"I do not have  to do anything," Mycroft huffed indignantly.

You frowned at him, staring for a long while. "Fine then," you finally said, turning around in your seat. "I'll just leave you to figure it out on your own." You stopped, for effect, then added your pièce de résistance. "Too bad you don't know anything about Harry Potter, though, because that's the only way you'll be able to get anywhere with this murder."

You heard Mycroft turn to look at you, but didn't look at him, hiding your smirk. "What do you mean?" he asked cautiously.

"Me? Oh, nothing, I am after all only a civilian who would compromise the investigation of the oh so great and mighty-"

"Alright, alright," Mycroft sighed. "You've made your point. Now tell me what you know."

"What I know that you don't?" you repeated, enjoying this thoroughly. You practically heard his grimace at your words.

"Yes," he all but spat out. "Tell me what it is I don't know."

You turned back to face him and smiled. "Alright, but on one condition."

Mycroft groaned.

"You have to tell me why  you want to know," you continued, ignoring him. "Because you clearly aren't a police officer or an inspector, I can tell just by looking at you. So why do you have these photos, but more curiously, why do you care?"

Mycroft thought a moment. What harm could it do to tell you? It didn't endanger anyone's security, after all. "If you must know, I have a brother. He tends to forget which of us is the intelligent one and likes to be a smart aleck about it."

"So you put him in his place by solving revolting murders?" you prodded.

"Well, we-"

"No, no, it's fine, you don't have to explain. Sibling rivalry is a completely normal and justified reason to consult files and documents on the most gruesome and violent assassinations. I should know," you added mysteriously, although Mycroft couldn't quite tell if you were teasing or not. "Anyways, let's move on."

"Yes, let's," said Mycroft, having had quite enough of talking about his brother.

You cleared your throat before launching into your explanation.

"Alright, so the Deathly Hallows mark is obviously a tattoo. BUT, here's the thing, the skin around it is extremely raw. There's clearly some inflammation, which indicates it is probably infected, and thus was recently done in an unsterilized environment. So, how long had this man been dead when this picture was taken?"

Mycroft rummaged through his papers. "Three days," he said finally.

"I would surmise that this tattoo was made after his death by the murderer, as a brand of sorts. Where were these taken anyway? It looks rather dark and gloomy."

"The body was found in the sewers. The curious part was the weapon used. It was a sharp metallic object, most likely a dagger or sword, but it was imbibed with snake venom," Mycroft said.

"What?" you said.

"Yes, snake venom was-"

"No, no, I heard you perfectly. I was just shocked is all," you interrupted. "Well, this is an almost exact reproduction of the destruction of the diary, which was one of Voldemort's horcruxes, in the Chamber of Secrets, with Harry using a Basilisk fang to do it."

"Everything you just said was complete gibberish to me."

"Well, it doesn't really matter. You're most likely looking for a younger woman who was very close to the victim, confided everything in him, and he ended up using it to control her. Perhaps a girlfriend or a sister, needless to say someone who is a Harry Potter fan. Inspired herself from Ginny Weasley's story to destroy her own tyrant. That's the thing about vengeful murders. They always have to make it so personal," you concluded.

Mycroft looked at you, absolutely flabbergasted. "That was...extremely impressive."

You smirked. "Well, I do my best." You glanced out the window. "Oh, it seems we're arriving."

"Are we?" Mycroft asked. "That means I'm expecting someone."

People started to rise to fetch their luggage. You stood up. "I don't want to keep you from whomever you're meeting, so I'll skedaddle." You held out your hand. "It was nice to speak with you, Mike."

Mycroft stuck out his hand to shake with you. "Likewise, Y/N. It was a-" But Mycroft stopped, eyes widening, looking down at your hands, feeling something being pressed into his palm.

You bent down toward his ear and whispered, "I think we'll see each other quite soon, Mr. Holmes." With that, you let go of his hand, grabbed your bag and walked away, quickly getting lost in the crowd.

Mycroft stood shell shocked. It had been you, this whole time. He felt the hands of the secret service agents escorting him off the train and into an awaiting jet. Once he was aboard, he glanced down into his hand, and let out a chuckle. The neon pink USB key practically glowed in his hand.

I hope to see you soon, Miss Y/N.

Greetings my wonderful buttercups! I hope you're all very well and happy! Sorry about the long wait, but you know me, there's never really a short wait between updates... :/ Anyways, thanks for still putting up with me, and I hope this imagine was okay, even though I feel it kind of slipped from my grasp.

Lots of love (as always),

Helen