As soon as John entered the lab, he knew his life was about to change. All he didn't know yet was whether it was for bad or worse. He had met Mike Stamford around lunch-time and had gone for a drink with the man. After a chat, Mike had told him that a friend of his was looking for a flatmate. John should've known he should never have gone with Mike to meet this friend.

When the doors swung open, John had a clear view on the woman, bent over the aluminum table while delicately dropping a liquid in a petri dish. She had full lips, beautiful dark curling hair that touched her shoulders, but her cheekbones were unusually sharp as were her eyes. She had penetrating grey-blue eyes that saw through John in seconds. Yes, he should have known.

She was dressed in a suit, consisting of a black skirt and a tight-fitting jacket, her blouse perfectly white, high heels on her feet. She looked like a woman working in an office, her long fingers perfectly capable of typing quickly. She turned out to be a detective.

"Mike, can I borrow your phone? There's no signal on mine," she had asked after a quick glance at John. Her voice was lower than a normal woman's voice, but somehow John had been intrigued from the start. It suited her.

"Sorry, it's in my coat," Mike had answered, his eyes glued on the woman in his lab. John had sighed inwardly. Of course, she has many admirers.

"Here, use mine," John had suddenly found himself saying. It turned out to be the best thing that had ever happened to him.

Life with Sheryl was never boring. In fact, Sheryl was the only woman John knew who could run around London all day, or night for that matter, on high heels without twisting her ankle. Or, if she did, she never let him know. And to be honest, John was only too happy to run with her, solving crimes, meeting new people.

There was detective inspector Greg Lestrade: an elder man who was the only man John had met who wasn't completely blown away by Sheryl's looks or deductions. Perhaps that's why she liked the man, but she never showed. He let in her into cases and she tried to solve them. Well, trying wasn't the right word. Succeeding would be closer. If John had been looking for a quiet, civilian life, with Sheryl he definitely was on the wrong address. No, John loved it. He loved every second of it. She gave him the thrill of the chase, the excitement of the investigations and the will to live a full life again.

Mike appeared to have a very pathetic crush on Sheryl. He reminded John of a puppy, a lovesick teenager. Sheryl had noticed of course, and used it very skillfully.

Molly Hooper was the pathologist, a shy girl who didn't say anything, but who came in usefully when Sheryl needed a body or a microscope.

Anderson and Donovan were different. They didn't hate Sheryl, but weren't overly fond of her either. When she came in on the crime scenes, Anderson often looked at her and coughed disdainfully. Donovan was jealous, that was completely obvious.

They have had some very interesting cases, during which John learned more about the woman Sheryl, his new friend and flatmate. Bit by bit he began to understand her, but somehow she managed to surprise him. On these cases, they often met people who assumed they were a couple, which made John snigger all the time. Imagine that: beautiful Sheryl, with her curls, long legs and tight buttoned trench coat being in love with short, army-doctor John "Plain" Watson? Not that he minded, really. He loved to be with her, and he loved the running and the thrills, but nothing more. He was pleased, and honored, to be friends with this spectacular human being. Although he had to put up with the body parts, the noises, the violin at half past one in the morning, and the brother. Mycroft Holmes. John had a sister, Harry, himself, but never would he be so overly protective on his younger sister. He kidnapped John once or twice a week; interrogate him on Sheryl's health, her cases and how she was doing in general.

Normally Sheryl was fine. The cases kept her busy and sharp, but then the boredom attacked. He had never seen her like that and he was, in fact, worried. He had met many female soldiers in Afghanistan, but never a woman who fired at walls, indoors, with John's gun. Mrs. Hudson didn't really seem to mind. She adored Sheryl as the daughter she never had, and Sheryl had adopted her as some sort of mother. No, Sheryl was different, and John knew. Perhaps that was why he always forgave her. Those eyes could look so pleading at John; he knew he was being manipulated but she was his flatmate and living with her was wonderful. So he threw away the head and fingers and turned the telly on, sipping from his cup of tea while Sheryl lay on the sofa, complaining about how extremely dull London was.

When John had returned at Baker Street later than normal after a date with Sarah, he found Sheryl asleep on the sofa, dressed in pajama bottoms and a baggy grey t-shirt. John stood in the doorway, looking down on his flatmate. In the low light from the streets he features were softened. Her face was restful; a small, dreamy smile darting around her lips. The dark unruly curls spread over the armrest of the sofa, and John had to fight back the urge to stroke them.

He did notice, however, her face was paler than normal and she had bags, barely visible, under her eyes. She looked vulnerable. Sheryl never looked vulnerable.

Sheryl's eyelids fluttered a little, and sleepily she asked him: "home already? How late is it?"

"It's almost twelve," John answered, still standing in the doorway.

"Oh!" Sheryl jerked up, entirely awake, and walked towards the table where she fiddled with some test tubes and the Bunsen burner. John sighed. "Sheryl, you need to sleep," but she didn't answer him.

"Sheryl?" John's voice was tinged with impatience, and Sheryl noticed. Her curls danced around her head when she turned to face him.

"Sheryl, you look a mess! You need food and sleep."

Still she didn't answer him.

"You are getting paler by the day, especially the last few days. Are you okay?" John felt a lump forming in his stomach. What if something was wrong?

"I'm fine, John. Go to bed." She focused on her experiments again, the conversation being over in her eyes.

"No." John folded his arms and waited for an answer.

"John, I'm fine." When Sheryl saw John was waiting for an answer, she snapped: "you're a doctor. Deduce it."

John looked puzzled when he stared at her.

Sheryl rolled her eyes. "I'm a woman. I'm grumpy and tired. I'm pale…" she looked at him expectantly.

It dawned on John. "Oh. It's your period. Gosh, I'm so sorry."

"Yeah. Well done, doctor. If you wouldn't mind to leave me alone right now, that would be splendid."

"Right, sorry Sheryl, I didn't know. I mean… Well, it's none of my business of course, but then you are very irregular. I haven't seen you like this for… well, never, actually. And I've lived here for almost three months."

Sheryl sighed again. "Exercise and stress can cause irregularities in a woman's cycle, isn't it, doctor?" She let the last word sound a little sarcastic.

"You need to do something about it, Sheryl. It's not healthy."

"Good night John."

Some days later, down, he found Sheryl sitting at the kitchen table, scrabbling down notes in her black notebook.

"Ah, John. Are you busy tonight?" she asked, not looking up but examining the dust in the petri dishes.

John looked at her, and noticed how perfect she actually was. Her slender body was covered with a perfectly suiting tailored jacket. Her skin-colored tights never showed any sign of ladders whatsoever. He shook his head and focused on what she was saying.

"Sorry, what?"

Sheryl sighed and turned her chair towards the small blogger. "John, I need to you to help me infiltrate. We have to pretend we are together."

"What? Why-"

"I told you, weren't you listening?"

"No…"

"Great. There is a party where, I have good reasons to believe so, a murderer is going to attack his next victim tonight. I need you; an extra pair of eyes could come in handy."

"Oh, ok." John didn't bother to ask any questions, everything would become clear later that night.

He was just about to go to work, when she called after him. "Do me a favor and buy yourself a smoking. Black-tie will do." John sighed when he walked down the stairs. Hopefully his bank account wouldn't protest too much.

That evening Sheryl ate something in fact, her cheeks not as pale as some days ago John noticed much to his relief. After dinner, both went to their own bedrooms to change and prepare for the night out.

"Shall I shower first, Sheryl?"

"Fine."

When John had put on his trousers and dress shirt, the doorbell rang and when Mrs. Hudson had opened the door Molly came up. The shy pathologist was carrying a velvet black box, which looked heavy.

"Shall I help you with that?" John asked, being the polite Englishman he always was.

"Oh, no, thank you," Molly giggled. "Is Sheryl in already?"

"Erm, yes," John answered, motioning to the bathroom. "I believe she has just finished showering."

At that moment the door opened, allowing the steam to escape. "Ah, Molly! You are here already. Will my room do?" Sheryl stepped out of the bath room, covered only in a bath towel. John swallowed hard and excused himself, almost running up the stairs trying very hard not to think about that image.

When he was completely and properly dressed he went downstairs. Sheryl sat on a chair in the middle of the living room, dressed in a blood-red strapless dress, her dark hair twisted up artistically. She faced the window, and Molly was busy with lipstick and eye powder and all kinds of make-up stuff. Curious, John walked round the two women to see what they had been doing. His breath stuck in his throat. Sheryl, noticing his reaction as always, rolled her eyes.

"You look beautiful, Sheryl!" John muttered.

"Well, I feel like some sort of dressed-up monkey. But hey, I need to suit the other monkeys eh?"

"Well, there you are, Sheryl," Molly said suddenly, putting away the brushes. "Careful with the nails, the varnish needs to dry properly."

"Thank you Molly. I don't think we need to ask John what he thinks about this. Make sure you bring your jaw when we leave."

John grinned sheepishly. "I'm just not used to seeing you like this. Sorry, can't help it. How will we be going?"

"Mycroft consented to borrow us his limousine."

"Ah."

When the limousine had driven away, Sheryl linked her arm in John's and smiled. "Pretend to be madly in love with me," she softly whispered.

John only smiled. That couldn't be too difficult, could it?

The host greeted them, his gaze gliding up and down Sheryl's body. John could practically feel her rolling her eyes, and he grinned again. Yes, tonight was going to be fun.

And it was fun. Sheryl was being polite and charming, acting normally almost. She, of course, attracted many men who wanted to dance with her, but she refused them all politely.

When John asked her why she did that, she answered matter-of-factly: "we're here to catch a killer, not to dance!", but when the music began to play, Sheryl pulled him towards the small space reserved to be a dance floor. John locked her in his arms and glided around with her. She leant closer and hissed in his ear: "the man with the tuxedo and the bald head: he is the killer. We have to distract him."

Both left the dance floor in a hurry and walked towards that man casually, Sheryl grabbing a glass of champagne in a swift movement. When they brushed past the murderer, Sheryl dropped the glass, spilling its content all over the man. Sheryl went into acting-mode and in quite a convincing way. She apologised to him over and over again, offering to help him. He consented to that and together they walked out of the room, John following from a distance. They disappeared around the corner, and John decided not to follow them.

He took out his mobile phone and texted her.

What do you want me to do? –JW

He waited for a reply, which arrived quite soon.

Go home; it might take some more time to fix this. –SH

You sure? You don't need my help then? –JW

Perfectly sure. Home in an hour and a half at most. –SH

Be careful. –JW

I will. ;-) –SH

John sighed, frowning a little over the smiley. Sheryl never used emoticons in her texts. He put the thoughts aside and left the building. Now he had to find a cab to bring him home.

Well, what d'you think? Continue or not? This idea has been in my head for quite a while now, and there are loads more for the two of them. Please review: it harldy costs any time and makes for a very happy author :D