Dedicated with many, many thanks to my marvelous Beta, Saturn-Jupiter. Any mistakes remaining are mine, not hers.
Sherlock was the spare.
He'd worked it out early. Of course he would. He might not be as brilliant as Mycroft, but he was not as stupid as his family seemed to think. If the blatant favouritism hadn't been enough to reveal the secret, one had only to reason through the situation. It was logical, given the quantity of resources invested in training up offspring, to maintain a backup.
The potential had existed, once, for the priority to be reversed. Mycroft might have been the test-run, Sherlock the finished product. At some point between his conception and his third year of life he or nature might have made the stretch, shaped his growing mind into something unparalleled. Sherlock hadn't been able to work out, yet, exactly what had gone wrong there, but for whatever reason the window had closed and he was left perpetually running behind his much older brother, utterly unable to catch up. Sherlock was a genius, but no matter how far he outstripped his year mates, or even his teachers, he was never the best. Whatever intellectual mark he met, Mycroft was always there first, and in better style.
Branching into arenas where Mycroft never ventured had done little to alleviate the problem. The violin had been a minor success; Mummy, at least, had been pleased, and it was something Mycroft couldn't do (or, perhaps more accurately, didn't bother with). However to their father music, like sports and hobbies in general, was a waste and a sign of character weakness. Intellect and work were the things that mattered. His victory over Mycroft in athletic prowess was thus turned to defeat as well. Sherlock's more physical nature had been a frequent source of trouble; he did his best to stifle it where he could. In every relevant area, Mycroft's shadow cut him off from glory.
It was maddening.
It wouldn't have been so bad if Mycroft had been trying. Losing hard-fought battles to a closely matched, more experienced but respectful foe would have been difficult, but tolerable. To be defeated by an opponent who not only seemed to expend no effort but seemed oblivious to the competition, on the other hand, was beyond humiliating. Even worse, half the time Mycroft tried to give Sherlock advice. Guidance. The winner was trying to mitigate the loser's abject failures.
That was the thing that had pushed him over the edge the night he had destroyed his brother's stamp collection. He hadn't intended to do anything quite so drastic, but his mood that day had been foul; Mummy was showing the signs of a budding headache, and at dinner Father had spoken exclusively to Mycroft, never once mentioning Sherlock or the science prize he'd won at the end of term. Then Sherlock had been sent to bed, while Mycroft was allowed to sit for hours in the study, carrying on his conversation with Father. When Mycroft had looked into Sherlock's room afterward and found him still awake, he'd complemented Sherlock on the award and gone on to the topics of behaviour in school and appropriate conduct for a Holmes, in precisely Father's usual tone and with many of his usual phrases. Sherlock resented his father's lectures; to hear one from his brother, in that condescending tone- it was simply too much. And while Mycroft's reaction had exceeded Sherlock's expectations to a frightening degree (they were only bits of printed paper, and Grandfather had been dead years), it was also a triumph, because finally, finally, he had reacted. Finally Sherlock had landed a blow.
The success had spurred him; he had been in exceptional form for several months thereafter, good by both his parents' definitions. He might have gone on in that futile vein indefinitely, had Carl Powers not perished in a swimming pool.
He knew there was something wrong; he could even identify the starting point for the investigation. No matter how often or articulately he raised his objections, however, Mummy treated him like a child with a nightmare and Father... Father had made his opinion clear. The spare was defective. No matter what happened, he would never be Mycroft.
He decided, then, that it was time to stop trying to be.
He abandoned 'good'. He said what he wanted to say, went where he felt like going, studied what caught his interest. His grades plummeted; the meagre social approval he'd garnered evaporated like morning dew. Father gave him lectures every night for two months, and then gave up on him altogether.
His proficiency with the violin skyrocketed.
His days began to brim with a positively manic glee. He was alive. The academic energy he had been wasting he now sank into experiments in his room, experiments so fascinating that most days he forgot to eat if Mummy didn't make him. With the tedious social niceties thrown by the wayside he could occupy his brain observing, cataloguing, testing the people around him. He explored parts of London where no Holmes had ever set foot, in styles of clothing no Holmes had ever worn, and when he had seen how people treated him he'd change his clothes and his speech and his walk and go again, and again. He discovered crime -decades of puzzles, most tawdry and obvious, but some... some delightfully challenging. And when the puzzles got old, well, crime led him to other things that could alleviate the boredom.
It was when Father died that it all started going wrong again. It wasn't that he missed the man; after all, he'd never been given more than a few minutes a day of Father's attention, and not even that of late. Besides, Mycroft was still around, a copy of Father in every last cold, corpulent, conniving, controlling detail. The golden boy made good.
The golden boy wasn't as tall as he remembered.
He'd noticed, vaguely, that his clothes had been replaced rather frequently of late, but somehow he hadn't used that fact to predict his new ability to look directly into his older brother's eyes. Oh, Mycroft was still a hair taller, but only a hair. Sherlock realised, as he gazed levelly into his brother s face, that a lecture from him would no longer have the force of his looming form behind it, grinding it in. Disdain could no longer collect in those eyes and pelt down, the condensed droplets, like stinging rain, gaining force in their plummet. They were equally matched in something, something relevant, at last.
With a head start of that size in growth, the corresponding one in education, the advantages in time and attention that came with being the first born... it was no wonder Mycroft had always been slightly ahead. Perhaps their abilities were not so distant as he had always believed. If a few feet had made this much difference in Sherlock's perceptions, Mycroft, he realised, had likely been seeing quite a different view all their lives. What would conversations between them have been like if they had been the same height all along? Or would they have been any different at all?
He sampled his memory for test cases and scrutinised them, taking this new variable into account; before long he was cursing himself soundly. He'd learned how to understand human behaviour (the ability to predict was a clear indicator of comprehension) by reducing it to categorised variables and making equations, algebraic strings he could manipulate to his heart's content. How could he have failed to apply that practice to his arch-rival? Could he really have been as blind as that? Mycroft was nuanced, complex... In analysing him Sherlock had been trying to practice calculus without a knowledge of negative numbers. Now all his answers were in doubt. Everything looked so different from the other side of the axis.
The rapid reweaving of nearly two decades of context and subtext dizzied him; for the rest of the day people talked at him, but he was too stunned and preoccupied to answer, to even process what was said. This was not a great problem, as he had no reputation for conviviality to jeopardise. He did wish everyone would leave him in quiet to think.
Quiet, when it arrived, didn't help. His whole balance was thrown off. School, always tiresome, became nearly unbearable. His mind no longer churned out an endless stream of engaging experiments; there were gaps, and in the gaps boredom would creep in. Mummy was ill with increasing frequency; her marriage had been cold, but not loveless, and Sherlock did not know how to fill the absence that trailed her now. Sleep fled from him, and he began to find himself, multiple days in a week, watching the sun rise from some forgotten London alley after a night spent listening to his own feet hitting the paving stones. Even chemical stimulation no longer accomplished what it once had. It was all wrong, and it was all because of Mycroft.
So when he woke up in a hospital bed with no memory of how he arrived there, his body barely hanging together, and Mycroft once more looming over him, he was not well pleased. He would have said as much, but the pounding in his head made sentence construction difficult and his nerves only responded appropriately to his instructions about one time in four. He was forced to content himself with mental tirades against short-sighted suppliers who didn't realise that poisoning clients with inferior grade product sold at luxury grade prices was not a viable long-term business strategy despite the increase in short-term profits, and against interfering doctors and nurses and psychologists and social workers and policemen who wouldn't leave him to die in peace.
He didn't die, and after a few days of gruelling recuperation death no longer seemed the preferable option. The medical and law enforcement professionals continued to hound him, but to his great surprise Mycroft fended them off as often as he allowed them near. He was always on guard, always looking bored but impeccable in that damned plastic chair beside the bed. He mediated every interview, asked sharp questions at every exam in that soft, pleasant voice that left people uncomfortable without knowing why. If he slept, Sherlock didn't see it. He'd thought he was the only one in the family with a talent for wakefulness.
He kept waiting for his brother to address the cause of his condition, to fall into his old familiar role so that Sherlock could take up his. He was still waiting when they released him from hospital and Mycroft's driver took them both home.
Mummy was overjoyed to see him well again, even if he was the surplus child. He would even hazard to guess that his brother was pleased. That deduction hinged on the expression for approval being virtually indistinguishable from the one for digestive trouble when appearing on Mycroft's face, but that did not strike him as improbable. It would, in fact, go a long way toward supporting his reinterpretation of his older brother.
It couldn't last, of course. Sherlock was still himself, and Mycroft was still Father, insofar as he could be. Fraternal affection did not prevent him from being pompous or overbearing or from squandering his intellectual gifts on sordid politics. It did not engender in him any zest or ambition that could function as common ground. After Mummy died they had only genetics left in common.
That didn t stop Mycroft from turning up like a bad penny, inserting his nose and his uninvited opinion into every facet of his younger brother's life. After every minor miscalculation or misadventure (the ones that required hospitals to put right, anyway), he was sure to come round, wheedling and sniping and pressuring people into giving him his way. Sherlock took extra care to reject his smothering guidance, and to puncture his overinflated ego wherever possible.
But, down deep (and he would never admit it), it was not entirely unpleasant to know that, if things fell apart, Mycroft would be watching. He was generally quite alone, but if he ever closed his eyes really needing someone, his brother would be there when he woke up.