A/N: This is loosely based on the anime Black Butler, but you don't need to be familiar with that to understand this.

Disclaimer: It all belongs to the BBC.

"Are you certain you want to enter into a contract with me?" The disembodied voice echoed around the shadow-filled room, making it impossible to know where he was.

Molly Hooper was trembling in fear but hoped, prayed that the demon would mistake it for shivering from the cold, strong wind coming through the open window. Why did I have to summon him in the middle of a windstorm? She took a deep breath, trying to steady herself, then two more when that didn't work. "I summoned you, didn't I?" she asked, cursing her suddenly weak voice.

"That you did," the unseen demon purred in her ear.

She jumped, she couldn't help it. Her would-be avenger chuckled darkly, the sound surging like lightning through her nervous system.

Is it possible to die from fear? Molly took another steadying breath. "Danny Forsythe is a free man while Tom … my Tom … lies dead and buried." She swallowed hard, fighting back tears. I've cried enough, it's time for action. "Kill the man who killed my fiancé and I'll pay your price." Belatedly, she remembered that she needed to close any loopholes. "As long as I don't die by your hands."

He chuckled again then purred in her other ear, "If I wanted to kill you, human, do you really think you could stop me?"

She shivered again, and she knew there was no mistaking it for a chill this time. "No," she admitted quietly, "but if you swear you won't, then you can't."

"You've done your research," he said approvingly. "Very well."

A whirlwind of crow feathers started swirling in front of her, moving faster and faster until a figure stepped forward from the center and the whirlwind vanished. The figure was a man, tall enough to tower over her petite frame, with curly hair as black as the feathers, eyes that were an impossible combination of blue-green-gold, sharply-defined cheekbones that a small part of her desperately wanted to touch, and fair, flawless skin that seemed to glow in the light of the single candle on the coffee table. He wore an expertly-tailored black designer suit, a white dress shirt with the first two buttons undone and the others straining, black dress shoes, black leather gloves, and a black Belstaff that billowed in the wind still whipping around her sitting room.

He chuckled at her wide eyes. The demon approached her slowly, like one would a skittish horse, then got down on one knee before her, like a knight kneeling before his queen. "Say the words," he murmured, gazing up at her, his eyes flashing red.

Molly startled at the sight then mentally shook herself. He's a demon, what did you expect? "Kill my enemy and you will have my soul when I die."

"No harm shall come to you, by me or anyone else. I will destroy anyone who hurts you. I will serve you in every way until your death, then I will devour your soul. We have a bargain," he murmured.

Removing his gloves, he took her left hand in both of his. His hands were warm, warmer than any human's, then Molly felt a surge of heat flow into her. It was pleasant at first, then she felt a red-hot burning in her chest. Molly fell to her knees, gasping in pain, barely registering the large, strong hands holding her by her shoulders. When the pain stopped, she looked down to see part of a marking, almost like a brand, on her skin over her heart, visible just above the neckline of her shirt. She tugged the shirt down enough to see the entire marking. It was a pentagram surrounded by and filled with strange characters she didn't understand.

"My mark," he murmured. "It's the symbol of our contract and it links me to you." He lifted his left hand from her shoulder and showed the back of it to her. On it was the same mark.

"How does it link us?" The reality of the situation was only now dawning on her. Oh God, what have I done?

"If you ever need me, put your hand over the mark and say my name, I'll come to you."

"What's your name?" I've made a pact with the devil and I don't even know his name...

He smirked. "My real name is impossible for humans to pronounce. Call me Sherlock." He helped her to her feet.

She took a few more deep breaths to steady herself again then looked up at him. Sherlock's impossibly-colored eyes gazed back at her intently. Molly felt stripped bare but there was no time to worry about that now. Danny Forsythe has escaped justice long enough.

"I gave you my word, it's time you started holding up your end of the bargain," she said firmly.

He nodded. "What will you have me do, Mistress?"

"First, that stops right now. 'Mistress' hasn't meant 'female master' since the Nineteenth Century." With everything that's happened in the past six months, you'd think that wouldn't bother me, but it does, dammit.

He smirked again. "What shall I call you, then?"

"Molly."

"A servant does not call his employer by her first name."

"I didn't agree to have you as my servant, that was all you. All I want is for you to avenge Tom's death then leave me alone until I die."

"A lifetime of service is an expected part of the contract. Your soul is worth much more than simply taking the life of a criminal. You deserve my service and you will receive it."

Where does a demon get off sounding so damn proper? "You're not-" she started to protest again but he raised an eyebrow. She sighed quietly. "Fine, you're my servant. If you're not going to call me Molly, then you can call me Miss Hooper, I suppose."

Sherlock nodded. Her eyes strayed down to the straining buttons on his shirt. Free the buttons! she thought wildly then she lifted her eyes back to his still-smirking face.

"I take it you like what you see," he murmured, amused.

Molly felt her cheeks burning but she ignored the sensation. "You're not here for that," she said firmly.

"I said I'd serve you in every way I can," he murmured. He leaned to whisper in her ear. "All you have to do is ask."

Molly groaned in frustration. "All I care about is Danny Forsythe getting what he deserves. Nothing else matters."

He raised an eyebrow as he assessed her. "You truly believe that. Very well, I am your servant. I will do as you bid me." He bowed to her, a low, formal bow, then disappeared in a swirl of crow feathers. As soon as he was gone, the lights in her flat came on by themselves and the window closed itself.

Molly stared at where he'd been. What in the HELL have I gotten myself into? The enormity of the situation hit her in waves. I made a deal with a devil, an actual devil… I asked him to kill Danny Forsythe in exchange for my soul… I'm going to be responsible for the death of another human being… Her eyes flit to the mantel above the fireplace, where she kept a framed copy of her and Tom's engagement photo. He was standing behind her, his arms wrapped around her, and they were both smiling and happy. No, Danny is the one responsible for the death of another human being – my Tom. The police botched up the evidence so the jury let him walk but he needs to be punished for what he did…

Her thoughts inevitably drifted to the night of the mugging and Molly shook her head. No, I'm not going down that path tonight. Bone-weary, she laid down on the sofa and turned on the telly, flipping through channels until she found a documentary about cats. Tom was so good when Toby died… I know that if he hadn't been allergic, he would have gotten me another cat. The narrator was talking about rival toms fighting over a queen when she started to doze off.

The telly suddenly turned off. Molly looked up to see Sherlock standing above her. His coat was gone but otherwise he was unchanged. He was holding the remote in one hand. Sherlock set it on the coffee table then sat on the sofa and pulled her into his lap. Heat radiated from him, making her want to curl up against him. Coming to her senses, Molly tried to get up but he held her firmly.

"Stop squirming," he murmured, smirking a bit. "You're only going to excite me."

Molly stopped struggling. "Did you kill him?" she asked quietly. At his nod, she asked how, then thought better of it. "On second thought, don't tell me. I don't need to know."

He nodded. "It's better if you didn't know my methods. Suffice it to say, he will not be able to hurt you or anyone else."

She felt her body sag in relief. Sherlock silently encouraged her to lay her head on his shoulder. "Thank you," she murmured, glad she couldn't see his eyes. "I've spent the last six months wanting him to face justice. When the jury acquitted him last month on a technicality, I had never felt so betrayed."

"That's when you read up on summoning demons." His voice was soft, soothing. "Now that that ugliness is behind us…" Sherlock's hands moved to the hem of her jumper.

Molly lifted her head to give him a disapproving glare. "Uh, no. We're not going there." She batted his hands away.

"I made a vow to serve you," he murmured as he nuzzled her neck. "What better way to serve you is there than this?"

What, indeed? But really, I can't do this… She gently pushed at his chest until he lifted his head, his eyes questioning. "I can't, Sherlock," she murmured. "Meaningless sex has never been in my nature. I'll let you serve me every other way, just not that." She moved to get up and this time, he let her slide off his lap and stand up shakily, not looking at him.

Sherlock watched her for a moment. "How long has it been?" he murmured.

She glanced at the photo on the mantle again. "Tom's been dead six months," she said quietly. "You know that perfectly well."

"How long has it been?"

Molly sighed heavily. "Eight months. The last time we'd had sex was eight months ago, then he started to feel all this stress from work and, well…"

"Don't make me repeat myself again, Miss Hooper," Sherlock said firmly.

She turned to stare at him. What? Then what's he asking? Oh… "Four years. Jim was nice and really good in bed, but I ended it when I realized he was just using me."

Sherlock stood up, his eyes locked on hers. "Why were you going to marry Tom if the sex, never good to begin with, was nonexistent?"

Molly laughed weakly, desperate to be rid of some of the tension rising in her. "Sex isn't everything." At his smirk, she insisted, "It isn't. There's so much more to love than just sex. Tom and I were there for each other."

"Four years without good sex." He shook his head in disbelief. "It's a wonder you haven't spontaneously combusted."

She glared at him. "Why are you so obsessed with my sex life anyway?"

He smiled a bit. "You haven't guessed? I'm an incubus."

Well, that explains it. In her research on demons, she had found lots of information on incubi and succubi, but none of it current. "If you're a sex demon, why are you making bargains?"

"Bored," he said simply. "It's hard to find women to seduce these days when everyone is already so debauched."

He's got a point. Of course, a lack of women to seduce is probably why he wants to get into my knickers so bad – I'm not exactly debauched. But it's still not going to happen. "So … how often are you going to be around? Once a fortnight?" She could hear the hopefulness in her voice and hoped she didn't sound too eager to be rid of him.

He chuckled, the sound flowing through her nervous system again, but this time all she felt was arousal. "Every day. Serving you means I am never far from you." She couldn't help feeling a bit panicked at that and he must have seen it. "Never further than the next room or so."

Molly relaxed at that. "I … I think we need to set down a few ground rules. One, you keep your hands to yourself."

Sherlock approached her, smirking a bit. "Are you certain you don't want to take advantage of my centuries of expertise?"

Centuries? Feeling her resolve starting to waver, she shook her head to clear it and said firmly, "I'm sure. Two, you're my servant but we can't let the outside world know about our contract. I'll say you're my-"

"Boyfriend?" he asked innocently, but his eyes were dancing.

"Butler." Disappointment flashed in his opalescent eyes but she ignored it. "I can say I won a year of your services at a charity fundraiser. There's no way my friends are going to believe it, they'll probably think we're dating anyway. Of course, they'll be concerned about me dating only six months after Tom." She smiled at him weakly. "Be prepared for lots of questions, especially from Greg, he's a detective inspector."

"So, I'm to receive all the suspicion a new boyfriend would receive, without the pleasure of actually being your boyfriend?" His voice was low and soft, making Molly think of black velvet.

She shivered then glared at him. "Yes. Please, stop trying to seduce me. I know you're an incubus and it's your nature, but you can fight your nature."

He leaned to murmur in her ear, "As you wish, Miss Hooper." At her continued glare, he went back to the sofa and sat down, crossing his legs and stretching his arms out along the back of the sofa, his eyes on her. "Anything else?"

Molly tried hard to ignore the fact that the buttons on his shirt were really straining now, but she could tell by Sherlock's smirk that he knew she was fighting a losing battle. "Three, we will respect each other's privacy. If you ask me a question I'm not comfortable answering, you will accept that. Also, privacy means my bedroom is completely off-limits."

"Very well."

He accepted that way too easily, Molly thought suspiciously. "Do demons sleep?"

Sherlock chuckled. "Out of necessity, incubi and succubi physiology is nearly identical to a human's. I don't need as much sleep, but I do sleep."

Molly could feel her scientific curiosity rising. "What about food? Injuries? Diseases? Can you be killed?"

He smirked. "Thinking of getting out of our contract already?"

She grabbed a pillow from the recliner and threw it at his smug face. "Just answer the questions."

He caught the pillow in mid-air then put it behind his head, smirking. "I can eat human food, but my only true sustenance comes from souls." Molly could feel the blood leave her face and knew he must have seen it. "I'm immune to all human diseases. I can be injured or killed, but it takes a lot more to do it than any human." He stood up then approached her again, saying softly, "Really, you couldn't have found a better protector."

Molly looked up at him warily. "But who's going to protect me from you?" I could drown in those eyes…

He chuckled softly then murmured, "I'm afraid that task falls to you alone. Are you sure you're up to it?"

Hell no! "Um, I have to be." She managed to smile weakly. "One of us has to be the grown-up." He chuckled again and she felt the tension that had been building up dissipating. "It's getting late. I'll, um, give you the grand tour then we should both get to bed." At his hopeful look, she smirked. "Separately. The guestroom is perfectly fine for you."

Sherlock leaned to murmur in her ear, "You're a cruel, cruel woman, Miss Hooper."

She laughed softly. Payback's a bitch, sexy. "Oh, believe me, Sherlock, part of me is furious that I'm not taking you up on your offer. C'mon, I'll show you around." She turned and lead the way to the kitchen.