A/N: Hullo there, and welcome to my first Sherlock fanfic. This story takes place after the season four finale, "The Final Problem." Rated M for future chapters, which will probably contain a fair amount of violence, adult themes, and some language. I hope you enjoy!

Disclaimer: This is a work of fan fiction using characters and the world from BBC's Sherlock, and is not a part of the official story line. I have no ownership over these characters or the world, and no profit is being made from this story. Many thanks to the Sherlock creators—without their brilliance, the magnificent adaptation of Conan Doyle's stories wouldn't exist.

Chapter One: An Unexpected Party

Margaret sat in the back of the fully packed college classroom, staring at the wall-to-wall chalkboard crowded with numbers. It was a long mathematical problem, filling each square millimeter of the board. At the top was a title: Extra credit! The students were already frantically scribbling on pieces of scratch paper, attempting to solve it. None of them would—even if they were given years to stare at it. No, no one in this room could solve that problem. Accept for Margaret, of course.

It was the first day. They were all freshman, anxiously trying to win favor of the Professor before the year began. Favoritism was always the deciding factor. Margaret lazily wrote one symbol on her paper before turning it over and continuing to look around at the class full of naïve students. She practically had a PhD in this subject, yet she was sitting here, pretending to be one of them, one of the ordinary. She sighed. Only for this one day. Even if it was an embarrassment to her ego.

Finally, the professor strolled in with an apathetic frown on his face, dark brown, slicked back hair, and a walking cane that he barely used. He just touched it to the floor as he walked, not actually using it for bodily support. She suspected that it was not, in fact, a walking cane, but something more to his character. He was dressed sharply—a Westwood, if she wasn't overshooting—and wore a silver tiepin that she immediately recognized.

He walked to the board and hurriedly wrote Professor Moran. She stifled a snort. Even the great consulting criminal could give himself away through sentiment. How interesting.

She zoned out for the next hour and a half, planning her next moves carefully in her head so she wasn't caught off guard. She could vaguely hear his thick Irish accent in the background, explaining simple math to ordinary people who wouldn't understand the importance of the laws, the sequences, and the patterns. He rarely stopped for questions. He never asked for answers. He just taught. Margaret suspected he wasn't planning on staying here for more than a day, either. She suspected he knew something of her appearance here in Dublin.

She didn't snap out of her trance until the classroom was clearing out. Images floated in and out of her mind, reminding her of what needed to be done, what she was going to do. She could hear the helicopters and the voice on the megaphone, scratchy with fear and worn from age. She heard the gunshot, the body slamming down onto the pavement, blood gushing from the wound in his head. She felt the fear, the... sorrow? And the anger. A wall slammed down over the memories, caging them in. Focus.

Allowing herself to float back into the physical world, Margaret stayed in her seat until every last one of the students left. Then she stood, pushing her glasses up her nose and slinging her bag around her shoulder, grabbing her piece of paper with the single symbol. She slowly walked down the stairs to the classroom floor. Professor Moran was sitting at his desk, apparently typing an email. She dropped the paper down onto his computer and didn't wait for his response.

"It's too simple," she sighed, tapping her fingers on his desk to a certain melody she had played earlier. "Of course, none of the people here could solve it if they looked over it a thousand times. But that's their problem. They're looking for a solution. Sometimes there is no solution… sometimes the problem is unsolvable." The professor flipped the paper over, revealing an O with a slash piercing it's rounded figure—undefined.

He hummed to himself-the same melody she was tapping, in time with the percussive bangs of her fingernails. "I didn't think anyone would notice that misplaced negative," he sighed, his Irish lilt familiar, yet chilling with everything that's happened since that fateful day so many years ago. "But then, you don't seem like just anyone. I know you've been following me, Ms…?" He trailed off, obviously asking for a name. He put his head on a fist, blinking slowly—a seemingly bored and unconcerned pose. But the sparks in his eyes told otherwise.

Margaret raised her eyebrows ever so slowly, exaggerating her every move. "You mean to tell me you haven't figured it out yet? You haven't guessed?" She thought it was a possibility, though she hadn't changed much over the years appearance wise. She supposed he was blocking the memory—she had seen the signs before. Margaret continued, "We've met before, you and I… It was a very memorable experience—for me, at least. After all, you were pointing a gun at my head, threatening to blow my brains out in front of my father."

She saw his brown eyes darken with shadows, the breaths of lost souls clouding the darkened glass of a window, and then recognition passed along those gleaming orbs. "Ah, hello again, Ms. Margaret Magnussen."

She smiled a feral grin. This was going to be such a good day. "Hullo, Professor Moriarty."

Sherlock Holmes was bored. Extremely bored. He sat in his chair, hands up in prayer pose under his chin, impeccably dressed with a tan robe over his dark suit. From the depths of his mind, Bach's symphony no. 15 echoed in the background as he strolled through his mind palace, looking for nothing in particular. He had been without a case for the past week. Of course, the lines still formed outside of 221B and client emails still flooded his inbox, but he had found nothing interesting. He had solved every case that came to him from his chair. His brain was under-stimulated and it felt dreadful.

Of course, John was there, but he was currently in the kitchen, attempting to make homemade baby food with the blender. Sherlock supposed he should tell John about animal innards that were previously mixed in the contraption, but this thought occurred a little too late—the army doctor was already pouring the mix of sweet potato and milk into a small bowl.

Rosie sat across from Sherlock in John's chair, playing with Sherlock's ear-hat.

"John?"

"Yeah, Sherlock?" he said, irritation seeping through his voice. Sherlock supposed the good doctor must have been talking for a while now. He was too bored to notice.

"I think now would be a good time to tell you that along with that sweet potato and milk mixture, you will also be giving your child traces of rat, pig, and horse intestines."

John dropped the bowl, his upper lip was pulled back in aversion as his hands shot up into the air. "Oh God! What the hell, Sherlock! You think now would be a good time to tell me this? You know I tasted this stuff, right?"

Sherlock couldn't keep the small grin from his face as he responded, "Well, how am I expected to know that? I'm thinking." His face quickly contorted back into his signature blank expression, laced with annoyance.

John groaned, muttering something about a case. "Why in the world did you feel the need to blend animal intestines where we make food?" John was emphasizing a large amount of his words—Sherlock was finding it quite bothersome.

Sherlock shrugged. "It was an experiment. There was a case a while back where a man killed and puréed his wife's insides along with other animals and proceeded to—"

"Okay, no! Child in the room, Sherlock!" He cried, gesturing towards little Rosie who was still fiddling with the flaps on that peculiar hat. "I don't want to know…. I'm going to go brush my teeth…" He mumbled.

Sherlock snorted. "You go do that."

He had only begun to hear the running of water when the door to 221B Baker Street shot open and a girl burst through, weary and gasping for breath. A series of deductions passed through Sherlock's head almost too fast for him to notice.

Late twenties, 166 centimeters, cab, east London, meeting with a …man—possible romantic attachment, large dog—yellow lab, wears contacts, plays violin, died hair, left side of bed, exotic perfume—not name brand, obvious book lover, composer, anxiety issues, not athletic...

"Mr. Holmes, I believe you've made a huge miscalculation," she exclaimed through heavy breaths.

He raised his eyebrows. This day might just get a little more interesting. "And what's that?" He said, his voice containing the tiniest hint of sarcasm. His fingers tapped that familiar melody as he awaited her answer between labored breaths. Finally, a name rang out through the tight quarters of 221B.

"Jim Moriarty."