(*= not a real pairing. WARNINGS: MURDER! Brief mentions of arson and abuse)

Sherlock didn't like this. Not one bit. He didn't like not knowing something. And he certainly wasn't pleased that you had, somehow, figured it out before him. He had his blue eyes fixed on you in a way that made you slightly uncomfortable. Instead of telling him that though, you used your best defense. A little snark.

"Is that jealousy I detect, Sherlock? I only did what you do. You taught me well, after all." Sherlock said nothing for a moment but finally turned his eyes away from you. "How? How did you deduce that it wasn't his colleague? The colleague had the means, motive, and the time." You gave a little shrug.

"Easy. The other professor may have had all those things, but he also had an alibi. You see, the other professor always pays a visit to a...a house of ill repute on Friday and Saturday evenings. He partakes in various vices, although the one we should be looking at is his weekend drug cocktail. Based on the time of death, the suspect would have had no physical way of committing the murder even though he was also in the building with the victim. Too many different drugs floating through his system."

Sherlock knew that. Of course he knew that! He was an addict. But the question was, how did you know that? How had you even discovered the professor's secret habits? How had you eliminated a suspect before he had? There was hardly any evidence to suggest it. "Anyway, I have to go. I have things to do. Good day, Sherlock. Let me know if you need me again." With that, you flitted out the door, leaving Sherlock behind, thinking.

"I think you've met your match, Sherlock," Watson stated, sipping his tea. Sherlock didn't reply. His mind going over the same question again and again. How had you outsmarted him? How had you beaten him to a conclusion? He pondered on this for what seemed like hours until his phone rang again. Another victim. His newest mystery would have to wait. He had a murderer to catch.

*short time skip*

Sherlock breathed a little sigh of relief when he looked at the smoking hole he'd left in the wall. Three bodies, no real leads, yet somehow, you'd been managing to find information and deduce something about each victim. It was never much, like the first suspect's weekend habits or the second victim's love for setting things on fire or the third's enjoyment of hitting his wife. It wasn't enough to completely solve the case, just to rule out a suspect or motive or two.

"Why don't you just ask her to help with the case?" Watson had suggested. Sherlock glared at his flat mate. "I do not need her help. I just need to think. I need to go to my Mind Palace." Sherlock practically plopped himself down on the floor and closed his eyes. He let his mind sort through everything he knew about the case. Who the victims were, how they were killed, and all the possible suspects. The pieces were fitting together like a puzzle, but there was a piece missing. Who or what in their lives to all the victims have in common other than having some sort of vice that be deadly?

Nothing was fitting and it certainly didn't help that you kept popping into his Mind Palace, taunting him with your presence. It wouldn't have bothered him if you were actually helpful, but you weren't. You were just standing there. It was like you were children, keeping that last piece of the puzzle out of his reach. A piece that you couldn't possibly have unless...

Sherlock's eyes flew open and he shot to his feet. "Come, Watson!" He darted out the door, barely stopping to grab his coat, hat, and scarf. As quickly as he could, Sherlock found his way to your flat. Your flat mate refused him entry, but handed him a note saying five words. To where it all began

Sherlock let his mind wander through all the scenarios in his head, all the places you could be. It didn't take him long to figure it out, of course. The first case you worked on with him. The victim had been found in the sewer tunnels connecting all of London. He briefly heard Watson thank your flat mate as he ran off. He didn't need to look over his shoulder know Watson was following. Adrenaline pumped through his veins. He was almost there. He was so close to solving this case. He just needed to get to you.

Just as he suspected, another victim was waiting for them. One glance at the body on the ground confirmed Sherlock's suspicions. The victim wasn't you. That meant...

"Oh good. I was beginning to think you'd never figure it out." You stepped out of the shadows, a smirk painted on your lips. "The great Sherlock Holmes. You know, I never expected it would take this long. I expected to be caught after victim number one as soon as Lestrade called you in. Three, well now four, bodies. I must say I'm...disappointed, Sherlock. I thought you were better than this. I gave you all the clues you could need."

You sank down into a squat to look over your handiwork. "Such a shame. This one's pretty. Still, it was inevitable." You stood again, your (e/c) eyes piercing into Sherlock's. "I congratulate you, Miss Y/L/N. You managed to convince me you weren't part of this. Right up until the end." Your smirk grew.

"But why?" Watson asked, "Why do it at all when you knew Lestrade would call Sherlock in?" Sherlock scoffed, placing one hand in his pocket. "It's obvious, John. Y/N wanted me to catch her. But why? Why go through all this trouble? Why kill so many only to be caught on purpose?"

"You're NOT THINKING!" you shouted, "STOP THINKING LIKE A DETECTIVE AND START THINKING LIKE ME! Like a...murderer," you whispered that last word, confusing Sherlock. A moment ago, you had seemed proud of what you'd done. Now, you seemed unsure. It wasn't any type of mental illness. No. This was something else.

"Think about it. What did all your victim's have in common, Sherlock?" you asked, "What were they?" Sherlock let his mind go over the facts of the case before looking down at the last victim. "Who is this?" You scoffed lightly. "My former friend. At least, I thought he was my friend once." Sherlock's brows furrowed. You hadn't known any of the others personally.

"What was his name?" You gave it to him with a smile. That was all he needed. He'd seen the name in Scotland Yard's files. He was once accused of assaulting a young woman, but there was never enough corroborating evidence to support the claim. Eventually, the young woman died of her wounds and it was ruled an accidental death.

"Your sister...he was responsible for your sister's death." You nodded. "My poor, sweet sister. All she wanted was to be loved. He was there for her. He treated her well...until he didn't. When he didn't receive any consequences, I snapped. I knew he would have to pay somehow."

"And the others?" You shook your head and clenched your fists at your sides. "More of the same. Victim 2 set a house on fire with an elderly couple inside. Ruled an accident because the woman had dementia. Victim 3 beat his wife. That alone wasn't enough. He was also responsible for the death of his previous wife, but nothing was ever proven."

All the pieces finally clicked in Sherlock's mind. You weren't the person who killed for the thrill of it. You were an avenging angel. You killed to get justice for those who couldn't get it for themselves. "And the first?" Sherlock asked and you looked sheepishly down at your feet.

"An unfortunate accident. He wasn't my intended victim." Sherlock nodded as you confirmed his suspicions. "You were intending on killing the other professor. My original suspect. I suppose he too was responsible for a crime and did not face justice." You gave him a nod. "Yes. You see, I didn't kill just to kill. But now it's done and I need to face my own justice."

Sherlock sighed. "You've already called the police," he stated. As soon as he'd seen you step out of the shadows, he'd figured everything out. The sounds of sirens confirmed it. What kind of Avenging Angel would you be if you didn't accept your own justice when it came? "Thank you, Sherlock." With that, you climbed out of the sewers and raised your hands. Sherlock and Watson climbed up in time to see Donovan slamming the door of the car. Your eyes met Sherlock's and you did something he didn't expect. You smiled.