Jessica Moriarty was dangerous. No one knew that better than Sherlock did. He had scars from her, both physical and emotional. Even before she set her sights on ripping him apart, breaking him, shattering him into so many pieces that only she could put him back together, if she chose to.
He knew how dangerous she was from the minute he saw her. She hid her thirst for violence, for blood and gore, well under layers of meticulously applied make-up, expensive clothing that had no wrinkles. Her mask was a perfectly put-together appearance of elegance, class, and civility. He could see the cracks in her mask. No one else could until he told them about it, and even then, they doubted.
It was almost a privilege, being able to get a glimpse of the face underneath. Her mask filtered everything, to the point where even her voice sounded like that of an angel. Had he not been able to see the tips of bruises on her forearms, bruises clearly inflicted by someone trying to defend themselves, or the drops of blood on the bottom of her heels, he would have believed it himself.
After a while, he began to ponder the idea she wanted him to see what she truly was, that she had no interest in fooling him about her true nature.
She'd been generous enough to confirm it one night, after a long chase through the streets of London, as she pressed him up against a cold brick wall, one knee on his groin and a knife pressing into his throat, drawing blood the color of her crimson nails onto of his pale neck.
"I bet you've figured out that I want you to know who and what I am." He could feel her lips brushing against his ear as she spoke. He knew the location and position they were in was intentional; meant to make him think of couples in dark, dim alleyways. Had it not been for the knife at his throat and knee pressing painfully into his groin, it could have been exactly that.
"It wasn't that hard." His tone is clipped and short. He's uncomfortable, although he's not entirely sure why. Normally, he wouldn't be this uncomfortable, but she wasn't normal. He didn't, couldn't, react the way he normal did with her. "You clearly only let people see what you want them to see."
"Oh, Sherlock, you're good." Jessica's eyes were dark, colored with something semi-unfamiliar to him. "But I bet you haven't figured out the why yet."
He hadn't. He had entertained ideas, but each was more unlikely than the next. The predatory smile that slipped onto the face of his nemesis told him she knew what his answer would be.
"Let me enlighten you, then." She drew closer, almost impossibly close. Her perfume smelled of the brand John sometimes came back to the flat smelling like after he had spent the night with his latest girlfriend, and under that, Sherlock could smell the soap and shampoo she used. Interesting. He hadn't taken her for the sort of person that would go for a floral-smelling shampoo and conditioner set.
"You see, I'm letting you in on a little secret here. Promise me you'll keep it. I don't really want to kill you." The knife at his throat was pressed down with more force, and Sherlock couldn't help snarling slightly.
"I promise."
The pressure eased a bit, but not enough to where he felt safe.
"Well, I let you see what I truly am because I've got a little plan. One that I know will work." Her voice was velvety soft, a slightly seductive note injected into it. "You and I, we're destined for so much more than this. You know it as well as I do. But, the problem is that you don't want to admit that you need me, that you'd be almost nothing without me. That you want me. Here. With you. If only to keep you sane for a while, keep your mind from becoming stagnant. The idiots, the boring people like your dearest doctor, they'll do that to you.
"But you won't come willingly, oh no. You're convinced you're good, you're… pure." She sighed for a moment, shaking her head. "And that's where the problem is. You need me, but I can't be with you unless you come over to my side. See things my way for a bit. And I know it's going to be a while, so I've got a little game planned. It'll be fun. This is how it works: I'll get under your skin."
He couldn't help shooting her a doubtful look.
"Don't give me that look, I know how to. I bet I already am. I bet your dreams have already been painted with reds, reds that make you think of me. But, that's beside the point. The point is I'm going to get under your skin, make you want me. You'll hate yourself for it, but you won't be able to stop yourself. You'll cave, too. You're a strong man, but not that strong. Then, we'll just rinse and repeat. This game of mine will keep on going, each round having a shorter and shorter time to complete, until you know you can't live without me. Then, then you'll come over to my side, and do you know what I'm going to do with you then?"
"Make me your lap dog I suppose?" He snorted. "If you really think that I wi-"
"You're wrong." Sherlock stops, giving her a confused look. "I'll kill you, then. I'll have no use for you once I've broken you. I won't need you anymore." Moriarty pulls away, and he has to resist the urge to grab her. In the distance, he can hear the police, hear John.
"I look forward to seeing if you'll be able to do so. I doubt you will."
"Oh, I will be." Her smile is both seductive and full of knives. He can hear someone who is clearly winded getting even closer, and as he reaches forward to grab her, she leans forward to plant a kiss on his cheek. He stops, frozen in his tracks, and she's gone by the time John gets around the corner. As he stands there while John begins to fuss and worry over him, he can't tell whether or not the area where she sliced open his neck stings more, or if where she placed the kiss does.
Ten months later, Sherlock slowly leaves the brothel, adjusting his scarf around his neck. One whore, one who looks incredibly similar to Jessica, counts her money before smiling and waving him away, thanking him for another good time.
Sitting on the rooftop across from that building, Jessica Moriarty smiles.