What If?

John sat in the cab with Sherlock, in his usual apparently necessary silence. A murder, man and a woman, married, living in a house in London. Apparently it was... Grotesque. He felt a sense of dread surrounding this case, and Sherlock had descended into his silent thought processes already, so no reassurance there. If there would ever be any reassurance from Sherlock, that is. He gave up thinking about the case, it was frustrating him some how, giving him a head ache. Staring out of the window, he glazed over and tried to forget about it until necessary.

He could swear to god that there was something flying in the sky, but not a plane, no. It looked just like a black dot. He stared at it, and his eyes went funny, maybe he was imagining things. Letting the stress get to him. Calm down, John, it's only a case like all the others, just relax.

They pulled up outside the flat, Sherlock bounding in through the front door before John was even out of the car properly. Always like this, he thought. He headed up the steps, passing Anderson's glare as he walked in. It was strange, the house had no forced entry, it seemed completely normal. There was a feeling of family as soon as he walked in, and he knew the sense of dread now. Children, they would have had children. Well why not, big house like this, he saw a collection of toys nearly spilling out of the cupboard under the stairs in the hall. A few building blocks, a race car, a very much abused action man missing an arm. A boy, most likely. Sherlock appeared from the next room, his face looking grave. This was strange, even Anderson was picking up on it, he looked questioningly at the consulting detective. Sherlock caught John's eye, staring at the toys on the floor.

"No sign. But, two boys, one seven and one five. The father is in the kitchen, he seems to have died while reading the paper, the mother upstairs, died while drying her hair." he paused for a few brief seconds, something he didn't do often. "John, I think you need to take a look at them."

John nodded, following him into the kitchen. He braced himself for blood, carnage, all matter of disturbing things he could think of... But no splattered red came into view. The room was clean, untouched, nothing moved at all. The man still sat upright in his chair, his back to them. A shock of brown hair, messy and slightly spiked. A thin frame, very thin, all arms and legs and very tall. John walked cautiously to the other side of the table, not disturbing anything. He then jumped, startled at what had happened to the face. A gas mask, there, on the face, the black glass over the eyes staring at him like those of a monster.

"Sherlock, what ar-"

"Right! Got ourselves a crime scene! Ooooh, interesting!"

And at that moment a man bounded in, a brilliant smile on his face and a girl wandering in behind him. A tweed jacket, bow tie, all in general shades of brown. Ordinary, yet very odd. As soon as he saw Sherlock, his smile disappeared.
"Oh my..." he muttered, wide eyed, running a hand through his messy brown hair. The woman, she stopped, her face falling too as she saw the poor man's body at the kitchen table. John felt the need to smile reassuringly at her, but she just stared back, tapping the stranger on the shoulder.

"Doctor, what is it?" she muttered, tucking a lock of her red hair behind her ear.
"I think you've got another fan." John said quietly, Sherlock nodding and rolling his eyes as he further investigated. About to check the mask, finger tips just milimetres away, the stranger jumped to life again.

"STOP. No, that's bad, very bad. They're infectious. Don't touch them. Unfortunately any one who's already touched them is dead, unless we can find the capsule, obviously."
Sherlock did as he was told, which was odd, and he stared at the stranger, puzzled.

"Who are you?" he asked, frowning in disbelief at how this stranger knew more than he did. It annoyed him a little, as all people who seemingly knew more than he did annoyed him.

"I'm The Doctor, and you all need to get out, now. Quarantine the people who've touched the bodies. All of you out, you too Pondy." he said plainly, glancing at the red head.

"Doctor, what's going on?" she asked once more, her brow furrowing in frustration as she folded her arms. She questioned him, she felt annoyance at him. Sherlock's eyebrows raised, slightly amused at her.

"Um, Pond, this is Sherlock Holmes, that is John Watson, and you all need to get out before you start calling for your mothers."