"Look, Scarlet, the word 'Dad' covers a number of different things. Yes, it means your Dad, the one who made you and shared his genetic material with you, but it's also the name of a role. Of a job. You live with me, you call me Dad. I do your homework with you, you've thrown food at me, you've screamed in my face, you've weed on me, you've vomited on me. As far as being your Dad goes, I'm fairly sure I am doing the job, even if my genes aren't yours."

Three.

Sherlock had been carrying Scarlet around on his shoulders for nearly an hour. It hadn't been intentional, he'd just been finding the perfect birthday present for John harder to source than he'd hoped. He wasn't even sure he knew what he was looking for.

So he wasn't in the best of moods when he was summoned to Whitehall to see Mycroft.

"What do you want?" he said, walking into Mycroft's office and looming in front of him.

"Have a seat, Sherlock."

"No."

"Sherlock…" Scarlet said from on his shoulders.

"At least put Scarlet down."

"We're not staying. What do you want?"

"Sherlock," Scarlet whispered to him, pulling on his hair.

"In a second, Turnip. Mycroft, can you make this brief? We have things to do."

"I need you to read this file."

"No, I haven't got time,"

"Sherlock…" Scarlet said.

"Stop wriggling, Turnip. No, I haven't got time, I don't answer to your call, I'm not a hired hand, and I'm not interested!"

"You're very grumpy today, aren't you?"

"Mycroft! I'm busy! If you want me to help and you can crowbar yourself out of your office for maybe two minutes you can come to my flat and talk to me there, but Scarlet and I are on important business…" he broke off, registering the sudden warm sensation that was slowly trickling down his back.

"Is something wrong, Little Brother?"

"No, everything's fine. We're just busy."

He turned around and marched from the room.

oOo

Four.

Sherlock sat opposite Scarlet at the kitchen table.

"Please, Scarlet. Just eat a few mouthfuls, and then you're done. Please."

She pushed her bowl away from herself a bit, and put her head down on her hands. "Nope."

"Just…" He looked at her untouched meal. "Just five more mouthfuls and we can call it quits."

"No."

"Aren't you hungry?"

"Yes. I want cake."

"Well you can't have cake. If you're hungry, you'll eat the food that I made for you."

"No. It's yukky."

"It's not yukky. It's not! It's pasta! You like pasta!"

"No. This pasta is yukky."

"Well eat it quickly and then you don't have to taste it for long."

"It tastes like sick."

"No it doesn't!"

"How do you know? You don't have to eat it! Only I do!"

He briefly registered the injustice of this. It was true that Scarlet was eating pasta, made by him, whereas he and John would be eating delicious take-away made by, well, anyone else. But it was Thursday and Thursday was take-away night and he looked forward to take-away food and beer with John, damn it!"

He summoned his courage.

"Scarlet, what I eat or don't eat is irrelevant. You have to eat some food so you don't get hungry tonight, so eat it."

"No."

"Scarlet, will you please eat your food right now!"

"No."

"That wasn't a question! It was a… it was a command!"

"No, you said 'will you' so that makes it into a question."

He stood up and turned away for a moment trying hard not to lose his temper. He turned back and leaned on the table.

"Scarlet, you will pick up your fork and you will eat your pasta now, or you'll go to bed without anything at all."

"No."

He leaned on the table and looked at her. "Scarlet! You will eat your dinner now!"

She stood on her chair and leaned on the table opposite him.

"NO I WON'T!"

"Sit down! Pick up your fork and eat just one mouthful of pasta! Do it now!"

She sat down. She picked up her fork. She picked up a piece of pasta. She looked at him.

He held his breath.

She flicked the pasta at him and it hit him square on the forehead.

oOo

Five.

Sherlock waited outside the school doors, waiting for them to open the door for him.

"She's in the office with me," the receptionist told him as he got inside. "Here, come on in."

Scarlet was sat on a little grey chair, looking sorry for herself.

"Are you not feeling well, Turnip?"

Scarlet got up and came over to him for a hug.

"She has got a bit of a temperature," the receptionist told him. "It's probably just a bug. There's a lot going around at the moment."

"Yes. Well, let's take you home, Turnip." He led her outside and across the school grounds. She shivered though it wasn't particularly cold.

"You're not well are you, Turnip?" He said to her. "Do you want carrying home?"

She nodded forlornly and climbed onto his back. Her head rested on his shoulder and he could feel her fever against his neck. He decided he'd walk quickly.

"What do you want to do when you get home?"

"Don't know."

"We could do some drawing, or get your beads out or put on a film…"

She stiffened and retched loudly. The explosion of vomit down the front of Sherlock's coat was impressive. He stopped walking and Scarlet started whimpering.

"I'm sorry!"

"It's OK, OK." He put her down carefully and brushed himself down a bit but then gave it up as a bad job. "It's OK, Scarlet."

He pulled her gently towards him and found a handkerchief to wipe her face.

"Do you still feel sick?"

She nodded and cried.

"It's OK, Scarlet, these things happen. Let's get you home. I'm going to carry you again, but if you're going to be sick, do you think you could tell me?"

She nodded again.

"OK, let's go home, poppet."

He kissed her hot forehead and picked her up gently to carry her home.

oOo

Six.

"So, salt dissolves in water too!"

"Yes it does! What's next on the list?"

"Sugar."

"OK, go for it!"

Scarlet emptied the beaker of salt water into the sink, and carefully cleaned it for fear of contamination. She came back and carefully poured two hundred millilitres from the jug of fresh water, and carefully scooped sugar into Sherlock's measuring spoon. She poured it into the water and stirred it.

"It dissolves too!"

"Yes! Tick that one."

"Is that why when you have it in your tea, you stop seeing it?"

"Yes, that's right."

"But sometimes there's a tiny little bit left at the bottom."

"Yes. That's because John doesn't stir it enough. Or because sometimes I put a bit more than two sugars in there. Do you want to see what happens if we keep adding the sugar?"

She nodded and spooned more sugar in, stirring it carefully until…

"It's stopped dissolving!"

"Yes. That's called super saturation."

"What's that?"

"That means that there's no more space between the water molecules for any more sugar!"

"Can you spell it for me?"

He did so, smiling at her diligence, and the fact that like John, she poked her tongue out when she concentrated.

"You should say exactly how much sugar you were able to put in before super-saturation occurs." He watched as she did so. "Now, what's next?"

"A key."

"A key?"

"Yeah. That's what it says. Look!"

"OK. I'll find you a key. You clean the beaker out again." He dug around in a draw for a key he couldn't remember the purpose of. "OK. Here you go."

She dropped the key in the water. Predictably, nothing happened.

"Is this because the water is super statue-thingy with keys?"

"Er, no. No, it's because keys, or the metal that keys are made out of are not soluble."

"Oh."

"Well, not in water anyway. You'd think that would be fairly obvious to Mrs Seetle. Otherwise people's keys would dissolve if they took them out in the rain."

Scarlet giggled.

"Then John would be locked out in the rain again."

"That really wasn't my fault! You know what? All this means is that this key isn't water soluble. It doesn't mean that the key won't dissolve in anything."

"What do you mean?"

"I mean, do you think it would be fun if we extended the experiment a bit? Maybe we could tell Mrs Seetle what liquid can be used to dissolve the key!"

"Er, well, John likes it when we stick to the actual homework when it's Science."

"Yes but this would be fun!"

"Are you sure you mean 'fun' and not 'dangerous'?"

Sherlock stood up and unlocked his supply cupboard. "It's well worth remembering, Scarlet, that some things can be both!"

oOo

She thought about this. "Have I ever done anything nice for you?"

He grinned and hugged her closely. "Every day, Scarlet, every single day!

This one happens a couple of weeks after 'Trees'.

John and Sherlock lingered towards the back of the crowd of parents in the playground so that they were out of the way of the noise and the bustle. The door of the year 3 classroom opened and they looked up. Children started filing out one by one to be sent to their waiting parents.

Scarlet's name was called and she jumped down the two steps and ran across to them. Her pig-tails were loose and there was a yogurt stain on her jumper. She dropped her bag and her lunchbox to the floor jumped around at them for hugs and kisses.

"Why are you both here? Isn't it Dad's day? John I mean? Can we go to the park? Look! I got this! I'm star of the week for my homework even though Millie said I'd done it wrong!"

She thrust a laminated certificate at John and shot off across the playground after one of her friends. Sherlock stooped to pick up the bags and John turned the certificate around the right way. Under the big picture of a star was a little hand-written note from Scarlet's teacher.

'Scarlet is star of the week for writing not one, but TWO excellent essays on superheroes. Well done Scarlet!'

"You made her do two essays?" John asked Sherlock. "That seems a bit unfair."

"I didn't make her do any essays. Wasn't it your homework this week?"

"Was it?"

"Mm. Maybe we should start paying a bit more attention to that sort of thing."

"Maybe. On the other hand, she got a certificate for it when she had no help at all. And I still haven't forgotten the homework that melted the table. Come on, let's go and meet her at the park.

They found Scarlet playing in her beloved playground, following her friends down the fire-pole. They sat side by side on a bench and John took Scarlet's schoolbag from Sherlock and pulled out her homework folder.

"Here you go, Superheroes, my Dad Sherlock. Huh. You're a superhero, Sherlock. Who knew?"

"I had a pretty good idea." He took the folder away from John and started to read. A huge smile slowly spread across his face.

My Dad Sherlock is like a superhero but hes real and not maid up. His special power is knowing when people are lying and when they've done crimes. He can sometimes know what someone is thinking to, specially if they are lying to.

He cant fly but he can run very fast and dose big jumps and stuff and just in the summer he got shot and my other Dad John said it was really bad and Sherlock got better even though it was bad. He was very brave and he got better very quickly so sometimes I think he might have another superpower which is getting better quickly. But sometimes he takes ages to get better one time he had a cold so may be not.

He is really grate though and he doesn't even need to turn invisible cos mostly if he wants he can just make people not see him. He says it's called blending in and I've seen it and it's dead clever. He can make people say and do things he wants them to and not just by wining but sometimes he does wine to.

So I think my Dad Sherlock is a superhero even though hes real and I think hes better than superman and spiderman and batman and all the others and in fact hes even better cos hes real and he actually does stuff in real life and not just on films.

So that is why my Dad Sherlock is the best superhero I can think of in the world. And I am very lucky cos I get to live with him and hes my Dad.