Sherlock scowls and jabs in his brother's direction with the violin bow, "Of course it was her – did you not see the blonde hair in the elastic band?"
Mycroft hums, "Did you notice the scars in his arm? That brings a whole new theory to light."
"Of course I noticed the scars," Sherlock plucks on a string, "I do this for a living, Mycroft. I am very good at what I do."
John tunes them out when they get like this.
Every so often, Mycroft feels it is his brotherly duty to come and bother Sherlock about some case or other. To be honest, John generally stops listening once he has a mug of tea in his hands.
It is his firm belief that tea solves everything (although he knows Sherlock would disagree).
They bicker over the slightest thing, just to one-up each other – from the best type of milk in tea to actual case-related issues.
As Sherlock gets louder and more violent with his violin and Mycroft sits smugly on the sofa eating chocolate digestives, John watches them.
John knows Sherlock better than anyone else. He thinks.
Not as well as Mycroft and their mother, certainly, but better than anyone who isn't related to him.
The thing is, short of the little that Sherlock has revealed about himself either verbally or through his daily routine, John doesn't really know that much about him, despite the fact that he has been living with the man for a good six months now.
He doesn't know anything from his past, apart from snippets he's gleamed from conversations with Mycroft, or his thoughts that don't revolve around murder, or his dreams. If he even has them.
He doesn't seem to do things like a normal human being. He sleeps at irregular intervals and for periods of time that can last from half an hour to two days, he rarely eats in front of John (and John has his doubts about whether he really eats at all), his caffeine consumption is ridiculously high for a man so young and energetic and he has an addiction to nicotine patches.
In his professional capacity as a doctor, he is concerned and watches out for signs of crashing.
In his informal capacity of roommate and friend, he is extremely worried, but knows that is something bad does happen, he probably will not be able to prevent it, only deal with it once it happens.
But watching him now, watching fingers tighten on the bow when Mycroft touches a point he's sore about, watching eyes narrow but mouth stay in the same line as before as he thinks through his argument, watching him tap his foot impatiently, waiting his turn to speak, John thinks that the knows self-proclaimed (and, if he's honest, aptly described) genius better than anyone else.
Mycroft is more "human", if you will. He is easier to read, his posture is more open, he knows when to speak and when to stay silent. To the casual observer, he is normal. But John has spent a lot of time watching him as he argues with Sherlock, and he knows that everything about Mycroft is studied, calculated to some degree.
His words, the way they're expressed, the position of the eyebrows – everything is thought through. His appearance is meant to lull everyone into a sense of contentment so that they don't suspect he is anything like he really is. More like Sherlock.
John thinks that a lot of what Mycroft is and does comes from needing a sense of control of the world around him. He doesn't enjoy authority (he would be higher up, politically speaking, if he did), and he doesn't want power over people. Just over his situation, his life, and sometimes, the life of others. Such as his brother, and those who are (lucky enough? Unfortunate enough? Who suffer through the daily trials of being) a part of his life. It's a different kind of power.
Mycroft needs to know what is happening, and he needs to know that he is the one in control.
John snorts into his tea as his brain supplies the image of Mycroft in leathers wielding a whip.
Sometimes, John wonders what it would be like to live with Mycroft, but he comes to the conclusion that the man has idiosyncrasies that are worse than Sherlock's. Maybe he keeps entire corpses in the freezer, next to the Cornish vanilla ice cream and the frozen peas. Corpses of well-known criminals and lesser known political opponents. Maybe he would stalk John even more than he does now, using his job to keep tabs and check on everyone around him at the hospital. Or maybe he likes seafood. No.
Not that Mycroft has ever expressed to needing or wanting a roommate, but if he did, John would stick with Sherlock. Definitely the devil you know.
"Alright, so if I concede that the blazer's pocket was more important than initially thought, will you go away? Some of us have jobs that require attention."
John doesn't bother mentioning the fact that Mycroft basically runs the country.
He stares down into his tea.
Mycroft stands up, tapping his umbrella three times on the floor before nodding at him, telling Sherlock to stay well and departing, pulling on a scarf that he hadn't noticed earlier.
John's tea has gone cold.
Sherlock starts playing Stravinsky.