John was sixteen when his Link emerged, so he was luckier than his sister Harry, whose Link began when she was fourteen. Driven to distraction by the second set of emotions pressing at her own thoughts, she'd left school, like so many early emergers, and then turned to alcohol despite the efforts of her Link counselor to help her stabilise. Maybe John was supposed to be excited to emerge, like many of his schoolmates, who daydreamed about Fusing with whoever was on the other end of their link within days and spending the remainder of their lives with the bliss of a united mind, but after Harry's emergence he couldn't see it that way.
It began when John awoke in the middle of the night to a piercing headache unlike any he'd had before, a diffuse pain that had his whole skull throbbing. Oh no, he thought, please no, just a few more months, just until GCSEs are over. Secretly, John'd been hoping his Link wouldn't emerge until he was eighteen or even later, would let him at least begin uni before he'd have to manage the disruption. But this headache felt like the textbook example of Link emergence, just like the school's counselors described it.
John lay there for what felt like hours, nauseous with anxiety and apprehension. He hoped the girl whose emotions he'd be feeling all too soon was nice. He hoped she didn't feel too intensely, didn't veer from glee to despair to annoyance like some of the more dramatic girls in his class. Maybe her own Link to him had already emerged; maybe she was already meditating, doing calming exercises, trying to keep his own mood swings from ruining her GCSEs. Of course, she could already be in uni, or she could be younger than him. He hoped she wasn't younger; he'd hate to be putting anyone through what Harry went through, let alone someone whose mind he was destined to share, someone he would love.
The end, when it came, was extremely anticlimactic; the pain had gradually ebbed, leaving behind not the whirlwind of emotions he'd feared, but something like loneliness. John poked at the new and unfamiliar sensation; he could tell the feeling wasn't his, could feel his own nerves and exhaustion running parallel to it, but he couldn't make it recede, couldn't stop thinking about the loneliness. But it was quiet, somehow, worn, as if … as if whoever was feeling it had been feeling it for so long it barely registered any longer, he decided, and immediately a sympathetic pang of sadness ran through him. He'd meet this girl, someday, Fuse with her, and he didn't want her to feel lonely, not ever.
This was what made having a Link so dangerous; what he felt through the Link seemed impossible to ignore, made him forget his own worries. He should go wake his mum and dad, have them keep an eye on him until the morning, when they could call the school and make an appointment for him with a Link counselor. That was the first step. The counselor would help him establish some control and then he could begin to look. And when he found her, kissed her, Fused with her, neither of them could ever be lonely again.
Sherlock didn't tell anyone about the Link, and of course none of the unobservant fools who passed for authority figures around him noticed, because who expected a Link in a prepubescent? Mummy didn't notice, because Mummy already worried about him excessively, so she didn't want to notice anything else worrying, which made it easier to conceal from her.
Mycroft would have noticed, but he was off at university, and Sherlock didn't think Mycroft would tell on him, anyway, because Mycroft was the one who had given him the idea. When Mycroft's own Link had emerged (at the much more typical age of fifteen) he'd sat for one session with the counselor Mummy had chosen for him, locked himself in his room for a day, and when he'd emerged, had firmly declared that no more counseling would be required. True to his word, he'd betrayed not a glimmer of disruptive foreign emotion since.
And if Mycroft could do it, Sherlock would be able to master his Link even more quickly. No counselor would be required. He had, after all, read all the relevant literature on the topic, and surely understood it better than the overly empathetic simpletons who sought out Link counseling as a career.
Still, the actual emergence of the link was an upsetting experience, and he was glad no one would think it odd if he stayed in his room, didn't speak to anyone, and missed meals. The headache itself was bearable, no worse than when he got caught up in an experiment and went too long without sleep and food, or when he had no experiments and nothing to keep his mind from turning on itself. It was the anticipation of the link that was more unpleasant, and all his research hadn't left him confident of what was to come. He couldn't seem to stop himself hoping that whoever was on the other end of his Link wasn't a complete idiot, despite copious evidence, statistical and anecdotal, that most people were.
When the headache lifted and the new sensation of the link resolved itself into nothing more than the doltish happiness of someone complacently average, Sherlock didn't take the time to wonder why they were happy. It didn't matter to him. He would never find them, never Fuse with them. Once he had this mundane distraction under control, he could go on being extraordinary. And he'd do it all on his own.