Sherlock knew John was mad. Mad at him, yes, but more mad at himself.
It had been a particularly gruelling case that had lasted for almost a week. Sherlock had been either in deep concentration or running around London for the entire time. John had slept most nights, but Sherlock hadn't slept during the entire case and hadn't eaten more than the occasional piece of toast. It all caught up to him in the most inconvienient time: right as they had finally spotted the criminal and were chasing him down. John had been ahead for once, being closer to the suspect at the time, and hadn't seen Sherlock falter, or he would have insisted that he sit down, and rest.
As it was, Sherlock had kept going, ignoring his body's needs as only he could. He was only faintly aware that he was running slower than usual, and that he'd been almost shaking with exhaustion, and as a result he had worked himself into a collapse, cursing his transport as his knees buckled and he fell against a brick wall.
Lestrade had arrived twenty minutes later -his timing impeccably slow, as always- only to find his suspect subdued by John, who had trussed him up better than a turkey, and Sherlock a couple blocks away, barely even conscious. He had tried to stop them from taking him to a hospital, but it had been a little difficult after he had lost consciousness. He was awoken later by John yelling about malnutrition and dehydration and how he was never going to miss another meal, which Sherlock knew John was only doing because he blamed himself somehow, but it didn't stop John from doing it. And now Sherlock was stuck in the flat , forced to rest. To add insult to injury, Lestrade and John were now leaving to the Yard, and trying to convince him to babysit.
Babysit. Of all things.
"Come on Sherlock, it's only for the day. I swear she won't bother you much. You won't, will you Avery?" he asked, looking at his daughter. She nodded and smiled at Sherlock.
Sherlock rolled his eyes. "And how do you know I won't use her in one of my experiments?" he asked. He wouldn't, but Lestrade didn't need to know that.
"Because if you do, I'll never give you a single case to work on ever again." Lestrade answered. "Please Sherlock, I would take her to her ordinary babysitter, but she's sick. I promise I won't ask this of you ever again."
It was a promise he would be breaking, although Sherlock wouldn't really mind when he did.
John and Lestrade left, leaving the flat empty except for the two figures by the sofa. Sherlock turned back to his computer, completely ignoring the girl in front of him.
"What are you doing?" Avery asked, leaning in to look. Being the second of two children, she was quite used to being ignored. But it didn't stop her for trying to get their attention.
Sherlock turned away. "Nothing," he replied coldly. Children, he thought. I don't understand how anyone can like them, they're so whiny and disruptive and stupid.
"It can't be nothing," Avery said insistently, jolting him out of his reverie.
"What did you say?" Sherlock asked, pausing in his typing.
"You can't physically be doing nothing. It's impossible. You'd have to be dead to be doing nothing and even then you would be lying down or something," Avery explained, staring him straight in the eye.
Sherlock stared. The girl reminded him of someone. The way she spoke with absolute confidence. The stubborn look in her eye. He thought it might be Lestrade, she was his daughter after all, but after a second he realized who it was. And he was surprised.
She reminded him of himself. And this was something that Sherlock had never seen before. Everyone else was either too stupid, too slow, or too dumb, but this child was bright. She had potential, unlike the rest of her hopeless race.
And so he explained all of what he was doing to her, every bit, and marvelled in the way she could listen attentibely to him for hours. He had heard that children were eager to learn, but he generally avoided them, considering them to be even duller than most adults. But he realised that he liked the unwavering attention. And he decided to do something he'd never done before.
He decided to teach her how to deduce.
John unlocked the door, then paused. He could hear voices coming from the room, deep in conversation. He snuck up the stairs and burst into the flat with Lestrade right behind him, only to see Sherlock talking to Avery. He glanced at Lestrade, bewildered. Since when had Sherlock talked with children?
"We're back!" John said, for a lack of anything better to say.
Avery started, then looked at Sherlock. Sherlock nodded almost encouragingly, which blew John's mind away. Who was this new Sherlock?
Avery tentatively stepped forward. "Rough day at work, Dad?"
John groaned inwardly. She didn't know the half of it. They'd gotten to the station only to see a mob of people blocking the entrance. They'd had to wait for an hour despite Lestrade working there, for the mob to clear up, by which time Lestrade had gotten some kid's juice spilled on him. They'd finally managed to get to Lestrade's office, only to find that his chair had mysteriously disappeared from his office, and Donovan somehow had an extra chair in her's that was being occupied by her niece. So they were forced to stand the entire time, and John was now desperate for a chair.
Avery looked at her dad for a while, during which John and Lestrade had exchanged confused glances, and then she had finally spoke.
"You've been standing the whole time, haven't you?" Avery said. "You have a chair in the office, why didn't you sit? You've waited in a crowd, you've been stressed, and ew, you've gotten juice spilled on you. How'd that happen?" she wrinkled her nose in disgust.
Or maybe she does know half of it, John thought. Out loud, he said, "Has Sherlock been giving you lessons or something?"
He was half joking, but Avery answered seriously: "Oh yes, he's really smart. He's teaching me how to 'deduce',"
"Because that's just what we need," Lestrade muttered sarcastically. "Another Sherlock. God help us,"
John snickered.
Avery tugged on her father's sleeve. "You didn't answer my question. Can Sherlock babysit me again? Please?"
Lestrade looked at Sherlock. "Have you honestly been using her in an experiment? Because she's the only person that has ever begged to spend more time with you,"
Sherlock scowled. "Of course not. She's just brighter than all of your officers put together. You should actually teach her something once in a while,"
"Well, is it okay with you?" Lestrade asked. "If she stays with you next time, I mean,"
Sherlock hesitated. He did enjoy having someone actually intelligent to teach, but she interfered with The Work. And The Work was the most important.
"Whatever," he said, turning back to the computer. Lestrade grinned.