A/N: This is my first Sherlock fanfiction =) I'm aware that it's slightly OOC, but I liked the idea, so…

John shoved open the door of 221 Baker Street and trudged tiredly up the stairs. It had been a long day at the clinic, and he was exhausted and hoping to take a nap before Sherlock decided to play violin, create an explosion, or drag him across London on a case.

To his relief, the first thing he saw when he walked through the door of their flat was Sherlock seated at the table, completely absorbed with his microscope. John was just walking past the kitchen, anticipating a long, peaceful, nap, when a loud crash sounded from the kitchen. He peered into the room and was shocked to see a small boy who could not have been older than four staring in distress at the plate of food he had apparently just dropped on the floor. Fortunately, the plate was plastic and the food was only carrot sticks and a peanut-butter-and-jelly sandwich, but the child was still distraught. A small cry of distress escaped the boy's mouth, and his lower lip quivered dangerously, as he crouched over the food.

"Sherlock... there is a child in the kitchen."

"Yes, John."

"What is a child doing in the kitchen?"

No reply was forthcoming; Sherlock Holmes was once again engrossed with whatever experiment he was doing at the moment. With an aggravated sigh, John turned back to the child, studying him curiously.

The boy seemed to have overcome his distress and was humming quietly to himself as he picked up the food. Sensing John's gaze, he glanced up at John.

"Who are you?" he inquired, the dropped plate forgotten in favor of this new curiosity.

"Ah… I'm John. Dr. John Watson. I live here. Who are you?"

"Matthew," replied the boy, as if that explained everything.

"Right…Matthew… what are you doing here?"

"Eating lunch."

"No, I mean what are you…"

But Matthew had already lost interest in the conversation and wandered over to Sherlock. To John's alarm, the small boy began tugging on the detective's pant leg to get his attention.

John hurried forward to rescue the boy before Sherlock could explode at him for interrupting his experiment, but, to his surprise, his roommate, upon seeing the boy, merely said calmly, without the slightest trace of anger, "What is it, Matty? Weren't you eating lunch?"

"It fell on the floor."

"Well, why don't you get some more then?"

"But you told me I shouldn't get the jam by myself or I'd look like Uncle Mycroft."

"Uncle… who? Sherlock, is that your nephew?" John demanded, shocked. There was another Holmes?

Sherlock, of course, ignored him and turned back to the experiment.

Matthew promptly resumed tugging on his pant leg. "Can I see? Can I see, Daddy?"

John's mouth dropped open and a choking noise escaped him. "He's… you're… you mean he's… you…"

"Yes, John. I am his father." Sherlock turned to Matthew and, as if John had not already had a bad enough shock, picked up the tiny boy and settled him on his lap.

A delighted exclamation escaped the boy's lips, and he leaned over to peer into the microscope. His knees dug into Sherlock's legs, but, other than the slightest twitching of his facial muscles, the detective did not protest.

At this point, John was rather surprised that he had not died of shock. He sat down heavily on his armchair.

"Ooohh bacteria!" exclaimed the child.

Of course Sherlock would have taught the boy how to recognize bacteria under a microscope, thought John with a slightly hysterical laugh.

"I assume," Sherlock spoke up, not removing his eyes from the little boy perched on his lap, "that you are finding the idea of my being a father amusing, John?"

"Well, it's just…" John managed, "you just don't seem like the… father type."

Sherlock looked affronted. "I am a perfectly good father, John."

John resisted the temptation to snort, though he did roll his eyes. "Which is why I have not heard of or seen the boy until today."

"Mommy wanted me to live with her," the child piped up, still gazing in fascination at the bacteria. "But then she died and I had to come here because Uncle Mycroft doesn't like Daddy. Die is when you fall asleep and you don't wake up, and your body except your bones goes away after a long time."

"Sherlock?" inquired John in shock.

The detective sighed. "Yes, John. I was married, however impossible that may seem to you. She left shortly after Matty's birth, and I did not see him. She died a few days ago, however, so now he is coming to live with me."

"But you didn't even..." John's voice trailed off, and he sighed. "Never mind." A child- Sherlock's child- living with them? The idea seemed ludicrous, yet here he was. And he could not imagine that it would be easy living with a boy who had Sherlock's genes. The boy would probably bring home dead animals to cut up and try to create explosions using Sherlock's chemistry set. Oh, and he would certainly want to come on cases. And carry a gun.

And knowing the detective, he'd probably let the boy.

The doctor sighed. This was going to be a nightmare.

Then Matthew said something to Sherlock about the bacteria, and, with a soft smile John had never imagined seeing on the man's face, the detective began to explain a concept of science, his arm wrapped protectively around the boy's torso to keep him from falling off his somewhat precarious position onto the floor.

And John could not help but smile despite himself.

Please let me know what you thought; it would mean a lot! Constructive criticism is welcome; I'd like to get better. =)

If enough people like this, I'll probably continue this, though probably not for a couple of months because I'm pretty busy at the moment. =)

-battlemaiden518 ;)