Title: Their Law

Author: starjenni

Disclaimer: Don't own anyone.

Pairings: Sherlock/Mycroft epic brotherly love.

Warnings: Uh, I don't know, deception maybe? This fic is fluffier than the fluffiest of rabbits.

Rating: T

Spoilers: For both series, all episodes.

Word Count: ~2000 words.

Summary: It was this law they made for themselves, a law that said: Pretend to hate each other.

[On Sherlock ringing him at Christmas Eve] "Oh dear lord. We're not going to have Christmas phone calls now, are we? Have we passed a new law?" - Mycroft, A Scandal in Belgravia

"Smoking indoors, isn't that one of those…one of those law things?" - Sherlock, A Scandal in Belgravia

"Killing people is against the law."

This should be an easy statement to explain, an easy thing to say, but with Sherlock - as ever - nothing is ever easy.

"So?" says his ten year old brother, yawning and putting his feet up on the side of the chair he is lounging in. It is tea time and Mycroft is attempting to resist mummy's freshly baked cupcakes sitting on the table nearby. Sherlock has already had three, the irritating little twerp.

Other people would find it unnerving to hear a young boy - who hasn't even grown into his hands and feet yet - say something so cold and uncaring, and in such a frank tone of voice, but Mycroft has been managing Sherlock for ten years now and the only thing that would worry him is if Sherlock started understanding.

"It's a law," he says. "Laws are important."

Sherlock rolls his eyes. "Oh, please," he says, in tones far too mature for his age. "Don't start with the lectures, you'll sound like father - "

Mycroft smiles. Sherlock just doesn't get it. "No," he says. "You are not understanding, Sherlock."

"If you're going to make some speech about how wonderful it is to be good, to be a hero on the higher ground, like we're in some second-rate crime novel - "

"No," Mycroft interrupts. He would lose his patience now if it wasn't so good to see Sherlock just not get it. "Because it's more difficult."

Sherlock stalls, Mycroft can see it even if his body betrays no sign of it. "What?" he says.

Mycroft shrugs. "Anyone can break the law," he says. "That's easy. What is difficult is working inside the law and still getting what you want."

Sherlock stares at Mycroft like Mycroft has suddenly leapt up and started doing star jumps.

"Laws are important," Mycroft says breezily, though he is thrilled to be getting Sherlock's full attention for once. "Laws make the whole game more difficult. Any mediocre troublemaker can break a law and achieve results, but only geniuses can work inside it and achieve the same results." He takes a sip of his tea. "Something worth pondering," he says.

Sherlock goes silent, which means he is thinking, really thinking. Mycroft gives in and takes a cupcake to celebrate.

Sherlock says, some months later, "I need to know the laws."

It is summer and they are sitting by the river in the meadows behind the manor, Mycroft with his nose in Machiavelli and Sherlock with his nose in 100 Top Murders. Mummy refused to buy it for him, so he stole it instead. Mycroft has been sworn to secrecy, and has kept it only because he doesn't want mummy to get agitated, not with her heart the way it is these days.

"We could make a list," he offers to Sherlock's comment.

Sherlock nods and they lay aside their books, spending the rest of the day memorising all the laws inside their mind palaces. Well, Sherlock's is a mind palace.

Mycroft's is a mind city.

There are - they discover - two types of laws. Laws that the world has made and laws that they will need to make for themselves.

The laws of the latter category are varied and complex.

Later on, they make a law concerning the two of them.

They break this law momentarily when Sherlock turns out to be alive after all. Mycroft wouldn't say he expected it, but he hoped for it. He comes home to what he expected to be an empty house, to find his still irritating little brother lounging on the sofa by the fire, drinking his brandy.

"A bit rubbish, this vintage," Sherlock says, when Mycroft enters the room.

Mycroft has to take a moment. He half believed Sherlock was dead. He stops in the doorway and puts a hand to his mouth.

Sherlock glances over the top of the sofa at him. "It's all right," he says. "There's no one here. And I assume your house is bug-free."

It isn't, but the living room is. Some rooms keep their bugs. To give certain associations and groups a false sense of security, an impression that Mycroft Holmes isn't really that clever after all. Mycroft is very careful about what he says and does in those rooms. But this room is free.

There is no one around, there is no one to see. They are entirely alone.

He takes two steps forward and Sherlock tilts his head up. Mycroft drops a kiss onto his brother's forehead, light and dry and barely anything at all. He keeps his mouth there for a moment. Sherlock's skin is warm, heated by the fire.

"You must have known," Sherlock says.

"Yes," Mycroft replies against Sherlock's forehead. "But I worried."

It was this law they made for themselves, a law that said: Pretend to hate each other.

They don't hate each other at all, quite the opposite in fact. Sherlock is Mycroft's weakness and Mycroft is Sherlock's. In Mycroft's line of work - and, to a lesser extent, Sherlock's - showing any sort of weakness means you are finished before you even began. So they made the law.

They have kept to it for a long time, and extremely effectively - even their mother thought they hated each other. It was not too difficult to create because they already had some degree of sibling rivalry, they just strengthened it, made it more complex than it really was. They pretend to detest the sight of each other, moan and bitch when the other is in their company, make nothing easy for the other, they only - and this is one of the strictest rules of their law - go to each other for help when the matter is extremely urgent, or if they barter for it, such as in the case with the Hounds of Baskerville.

They are convincing. An especially intuitive person with inside knowledge of the brothers - such as John Watson - would believe that possibly Mycroft cared more for Sherlock than he let on, but then he was always the less talented actor of the two. They are almost entirely convincing.

It comes at a price, of course. They deliberately ignore each other at times when they most think of each other, like on birthdays or at Christmas. They cannot really sit and just talk like they used to, before Mycroft went into the government and they made the law. Sometimes Sherlock will wish he could discuss aspects of a case with Mycroft, because often even just saying it out loud to Mycroft would make certain elements clear to him, and sometimes Mycroft will wish that Sherlock was sitting beside him by the fire, nattering about his life and making Mycroft forget his for a bit. Their minds are so alike that any true conversation, any moment when they can be them in privacy, is a joy, is like music, two melodies in perfect sync. But to be who they are, to appear what they are - ice men, cold and uncaring, not even caring about their own family - they must follow their pretence and their law. In public, or wherever they could feasibly be caught.

They have a few slips, but they know how to cover them up by now. Like in the mortuary, for example, when Sherlock guessed Irene Adler's death. They were in public, anyone could have come into that corridor, Molly, anyone. That whole cigarette sharing was a slip. The conversation about their shared cold hearts was the cover up. And a little reminder to each other - remember the law.

Sherlock has more leeway. Sherlock can bring friends and people who love him into his life. Mycroft has to be more separate, must be more separate, must spend more days and nights alone. He must follow the law - the world's law - to the letter. Sherlock is a little freer, though, after that first conversation when he was ten, he still tries to stay inside the law as much as possible, when he can.

It is almost annoying that he is the better actor.

Sometimes Mycroft dreams that Sherlock actually hates him, that their pretence has become reality, and he wakes up gasping, chest constricting. The only dreams worse than Sherlock hating him are when Sherlock is dead, because at least a Sherlock who hates him is a Sherlock who is alive to hate him.

He wonders if Sherlock knows about his nightmares. Or if he has ever thought about them at all.

But they are alone now. They can have a stolen moment of privacy. Sherlock tugs Mycroft's arm from the sofa to curl around his chest. Mycroft raises his head from Sherlock's head enough to say, "Sherlock…I'm sorry I told Moriarty - "

"I was counting on you to," Sherlock interrupts brusquely. "I knew how he worked. And I needed to have him discredit me, so that I could meet him on the roof, so that I could protect - "

John, Mycroft thinks first, and then considers this and replaces it with, Everyone.

"So I am forgiven?" he half-teases.

Sherlock drums his fingers on Mycroft's arm. "If you help me now," he says. "I want to bring down Moriarty's associates. I need you to help me do it."

Mycroft considers this, resting his chin on Sherlock's head. "What about the law?" he asks. He can't just give Sherlock all this help, not without Certain People noticing and commenting…

Sherlock's fingers tighten on Mycroft's arm, just a little, but noticeably. "I don't - I don't care about it anymore," he says at last.

His voice is so strained. Mycroft wonders how long Sherlock has been hating the law, hating the pretence, hating the fact that he can't just ring up his older brother and ask for his advice or have a simple conversation.

Mycroft has more to lose. Sherlock will be the one truly in danger, if they break the law. If his competitors, if all the people who want to see him fall, know he has 'made it up' with his brother…

But then, Sherlock is more than capable of looking after himself.

And Mycroft is tired. He is so tired. It has been going on far too long. He wants to help Sherlock, he wants to give his genius little brother all the assistance he can, freely and without penalty. He misses their conversations, misses watching Sherlock's brain tick.

"All right," he says into Sherlock's hair. "All right."

Sherlock squeezes Mycroft's arm and relaxes into him, and they watch the fire burn down into embers.

Most laws need to be upheld, Mycroft knows. But there are also some that need to get broken.