John Watson probably thought that only Sherlock Holmes, could have his older brother for an archenemy. It was a plotline too corny even for most action comics. The evil twin, plot, was something only Sherlock could consider acceptably dramatic. John was right, in a sense, Sherlock was very nearly alone in his belief the most dangerous man he would ever encounter was his own big brother. The only other man who rather enjoyed this belief, if he was far less willing to admit it than Sherlock, was Mycroft Holmes.

The truth was that their allegiance to different sides, served them better than any friendship ever could. They both lamented 'ordinary' people's inability to make even the most basic of deductions, but in truth, that too, served them well. The numbers of people who, for example, made no connection between Mr Holmes, the enigmatic umbrella wielding brain of Whitehall and Sherlock Holmes, the acerbic, cerebral blog detective.

Mostly, no one questioned why a seemingly harmless internet star and his flatmate, were on level five surveillance. Mycroft would have his reasons after all and they would certainly be official business, not a concerned older brother spying on his younger sibling.

Most of Sherlock's many enemies never worked out how he always managed to get away from them at the last second, regardless of how carefully they cornered him.

Whenever Sherlock hacked into the Government database, no one ever suspected it was to surreptitiously aid the central balance, rather than to cause trouble or steal information for his own cases, as was naturally assumed.

Then there was the day the British Premier almost brained his most senior adviser, not realising his little brother was in the next room.

...

...

Sherlock had been summoned to Whitehall by his least favourite type of client; one who preferred to remain anonymous. As it was laughably obvious who in Whitehall might need his help but not want to publicly admit it, Sherlock did not refuse the summons. It might be interesting to know what the Prime Minister needed that his own secret service couldn't deal with.

He'd been told to wait in a giant lounge outside a heavy oak office door. The sounds of a scuffle came from inside and Sherlock raised an eyebrow at the two men who'd accompanied him there. Were they not planning on checking whether the PM was being attacked?

"Just wait, sir." One of the two told him sternly. Normal behaviour from the country leader then, to seem to be having a fight in his office.

He might have remained confused and curious, but obediently outside in the hall, had a dull groan not reached him through the office door. He shot a more insistent glance at his chaperones, but they ignored him, eyes staring blankly ahead, ignoring what seemed to be clear signs of distress from inside the office...

...

...

Mycroft was used to dealing with the mood swings of the most recent incumbent to the leading office of Government. All of the Prime Ministers and their parties needed to be dealt with slightly differently, most had some strange quirk it was best the public didn't know much about. That their current leader suffered with frequent visits from the proverbial black dog, fell very much into that category.

The first time his bouts of severe depression had resulted in physical injury on Mycroft's part, a series of assistants of both men had tried to intervene, to calm things down and ensure the most important asset of the Government, that it wasn't going to happen again. Mycroft waved them all off, dismissing all but the PM himself from the room. It occurred to him, that there was a very simply solution.

If the PM ever showed his private problem in public, the whole of the Government would be on rocky ground. If he took his seemingly uncontrollable tantrums out on too many members of staff or fellow members of cabinet, it increased the risk of a leak to the press. If, however, there was only one person who really saw the wrath of the PM's occasionally darkened mind, then he could be sure he would never let it get passed him.

Mycroft didn't usually work so closely with the PM and cabinet, they were almost all insufferable pompous fools and Mycroft preferred languishing at the palace. He was after all, really only answerable to the Monarch. He soon got used to increased time spent among the cabinet, keeping an eye on the country's leader. He learnt to spot very quickly, when the mood was taking him. He would immediately remove all other staff and politicians from the vicinity and allow the tantrum to pass. Sometimes it involved him staring impassively while a grown man hurled juvenile abuse at him. Occasionally, it involved him dodging flying fists and office supplies, or even on one occasion, allowing the premier to almost break his arm, when he trapped him between his desk and chair to tell him everything had gone to hell in a handbasket.

He hadn't bothered to ask what that meant. He'd waited until the other man had calmed down, backed away from him looking utterly horrified, before Mycroft had poured him a drink. What the PM really seemed to like about Mycroft's methods, was his calm and unwavering ability to feign ignorance. The first few times, once he'd returned to a relatively normal state of mind, he'd tried to apologise for his behaviour, but Mycroft had merely given him a confused look and asked what on earth he meant. Just as no one saw the black dog, no one saw the man who stopped it getting out of the Prime Minister's office, by hook or by crook.

On one particular day though, Mycroft made a rather grave miscalculation. The PM was in a bad way, a young PA had brought him tea and had a tea tray upturned on her. Mycroft had only just moved quickly enough to knock the tray out of her hands and stop the smack the PM gave it, sending boiling water over her. He was so busy trying to calm her down and hand her over to the PM's assistants outside, who would talk her out of telling anyone about it, that he didn't notice the golf club heading for his skull.

The girl had just left the room, door closing behind her a fraction of a second, before a swishing noise had Mycroft spinning on the spot. He turned just in time to see the golf club swinging down. He turned his head to a less deadly angle, before it smacked into the side of his face.

Admittedly, it was not ideal. Mycroft gave an inward groan of indignation as he sprawled on the floor of the PM's office, pretty certain he'd just been given a minor concussion. Still, it was preferable to outright killing him or knocking him unconscious, as the blow to the back of his head the PM had intended, would have done. He made one vague attempt to get to his knees, before abandoning that path and staying still, waiting for his vision to clear.

The PM appeared quite mad. He stood over Mycroft, panting like an angry rhinoceros.

"Sir…" Mycroft tried, irritated by the faint slur and infirmity in his voice. "M-might I suggest you-"

"Shut up, Holmes!"

Mycroft sighed heavily. This was not going to end well. How stupid of him, to have allowed the girl to distract him. She was one PA, even if she had gone to the press, she was easily discredited. It had not been her potential security risk, concerning him though. Like a…normal person, he'd been distracted by how scared she'd looked.

He should have known something was wrong. The PM had been worried about some missing files. Mycroft had been somewhat concerned about those too, but he was reasonably certain they'd show up before drastic action had to be taken and was yet to take any steps. He had thought though, from the way the PM was talking, that he might have tried to hire a private eye. Mycroft did not like the secret service. He had chosen so far not to broach the matter, until he had more information to broach it with.

If the PM was so desperate he'd ask a single agent to investigate, then it was almost inevitable he was going to have a bad episode in the near future. It never took much to trigger them, sometimes it didn't require a trigger at all, but Mycroft had never seen one quite so severe. Ideally speaking, if he did have to encounter this disturbing manifestation of an unfortunate neurosis, he would not have done so from a point of incapacitation.

The PM backed off suddenly and for a brief few seconds, Mycroft thought it was over. A sudden swing sent the entire contents of the PM's desk flying, some crashing to the floor, some shooting across the room and bouncing off the walls. Mycroft didn't need to worry about the noise. Everyone outside had clear instructions, they were not to interrupt. It was only as the PM approached him once more, standing over him with a thoroughly deranged look in his eyes, a solid crystal paperweight in one hand, that Mycroft rather regretted his instructions. He also thought once again, that it might really be all over.

He made an abortive attempt to reason with the other man, which came out as nothing more than a groan. The PM raised his hand, seeming entirely unaware he was about to murder the man known to many as simply 'the British Government'. The man in question, was stuck, staring and trying to accept the fact he was about to meet such a humiliating end.

There was a clicking sound from somewhere behind them. As the PM's arm swung downwards, a shout from somewhere alerted Mycroft to their new company. His eyes widened in shock, as a hand gripped the PM's wrist and stopped his flying weapon, inches away from Mycroft's skull.

His saviour wrenched the paperweight out of the other man's hand and forced him backwards. He was just about to take similarly violent steps to subdue the mad man, when a voice from behind him stopped him in his tracks.

"Sherlock! Stop…" Mycroft breathed, a disbelieving smile crossing his pallid features.

Sherlock turned to him, then looked back at his attacker. The other man was cowering against his desk, staring at Mycroft looking confused and stunned, as though he had no idea what had happened to his advisor, or why a stranger was now standing so menacingly in front of him.

Sherlock shook his head, at a loss, before turning and crouching next to Mycroft.
"Alright?" He asked, voice quiet and devoid of his usual snarkiness.

Mycroft nodded, raising an arm and using Sherlock's shoulder to lever himself into a sitting position. His head swum and he swayed slightly, before steadying himself.
"Grade one concussion. Inconvenient." He muttered.

Sherlock grinned.
"Is he mad?" He asked, gaze flickering in the direction of the PM, without allowing him to see.

Mycroft shook his head, before grimacing, immediately wishing he hadn't. "No, he's ill. One of the best kept secrets of the state. Could I trouble you for a hand up, Sherlock?"

"Are you sure?" Sherlock asked, looking doubtful. Mycroft's head was bleeding, eyes unfocused.

Mycroft nodded and Sherlock stood, pulling him to his feet with him. Mycroft swayed rather drastically, but Sherlock held him still, without comment.

"Mr Holmes!" The PM burst out suddenly. Sherlock and Mycroft turned to him in unison. He grimaced at the sight of Mycroft's head.
"I…had no intention of…"

"And no harm done, sir, I assure you I was simply careless, it won't happen again." Mycroft stated blandly.

Sherlock stared at him, but stayed quiet. The PM looked torn between total confusion and gratitude, before he drew himself up and straightened his suit with dignity.

"I should hope not. Now who is this person?" He demanded imperiously.

Sherlock's mouth opened, vitriol on his tongue, but he winced as Mycroft stood on his foot, curtailing his indignant response before it escaped. Sherlock looked sidelong at him, wondering how he could possibly be letting the other man get away with it. He noticed Mycroft was smothering an almost sympathetic looking smile.

"Ah yes, that may have been where the confusion came in." Mycroft replied pleasantly. "Sir, I believe you hired a Private Detective to find the missing Nolan papers?"

The PM's bewildered expression cleared slightly, he glanced at Sherlock with a less unfriendly eye.
"Yes…that's true, a Mr-"

"Sherlock Holmes." Sherlock supplied, stepping forward an extending a hand to the PM. The other man took it, still looking somewhat confused. Sherlock being his private eye, after all, didn't really explain what he was doing there.

Mycroft smiled grimly.
"Yes, might I introduce you, Prime Minister, to the one and only Private Consulting Detective, and er…my little brother."

...

...

Mycroft suspected Sherlock had rather enjoyed the shamefaced look on the Prime Minister's face, when he realised why he'd been stopped mid-episode. He was grateful, naturally, that he had not been allowed to cause serious harm, but Mycroft had made it clear he did not intend for anyone else to be involved in the necessary handling of his condition. It was one thing though, to expect employees to ignore the sounds or even sight, of Mycroft being attacked by the Prime Minister. When the PM had unknowingly brought his advisor's younger brother to his office, it was possibly too great an ask, that he had not intervened. Mycroft couldn't really be held accountable for the detective the PM had not told him he'd hired.

"Is that really part of your job?" Sherlock asked in amazement, once he and Mycroft had left the PM alone.

Mycroft perched on his desk, holding his head in one hand as he swallowed a handful of painkillers dry.
"The running of the Government, is my job, so yes, this is unfortunately, part of it."

"What would you have done if I hadn't been here?"

Mycroft gave Sherlock a look which answered for him. The younger man's grin faded rather rapidly.
"Anyway, Sherlock, I must thank you for your timely interruption-" Mycroft went on, before Sherlock could think too deeply into the implications of his unofficial role.

Sherlock smirked. It never hurt to have Mycroft somewhat in his debt.

"Now I don't suppose by any miracle you brought your Boswell with you, did you?" Mycroft asked.

Sherlock laughed at that. "Yeah, he's downstairs, I don't imagine he'll be too impressed by either your handling of a mentally ill superior or the amount of painkillers you just took. Need a hand?"

Mycroft whimpered into his hands and thanked his lucky stars it was still a small number, who knew the impertinent detective and he were related.
"Thank you, Sherlock."