This is what happens when ideas get stuck in my head. If anyone else has a story like this I sincerely did not know.
John watches from the window as the older Holmes brother leaves the flat and enters one of his black cars (or his only one, John hasn't quite decided if there's more than one yet), trusty umbrella in hand. It hadn't rained in London for days and the forecast didn't predict any rain for another two. Not for the first time, John wonders why Mycroft is so fond of his umbrella.
After mulling it over and deciding he has nothing to lose, John glances over at his flatmate "Sherlock?"
The world's only consulting detective didn't look up from John's laptop but answers anyway "yes John?"
"Why does Mycroft always carry an umbrella? It's not like he needs it all the time and he doesn't limp so there's no need for a cane. So why does he bother to carry it with him everywhere?"
Now Sherlock does look up, a hint of a smile tugging at his lips "I'm surprised you finally decided to ask. There's no story behind it if that's what you're wondering. That umbrella is simply Mycroft's last resort, his insurance."
John's brow furrows "How can an umbrella be his insurance?"
Sherlock returns his gaze to the laptop "Mycroft had it custom made. I highly doubt there's another like it in the world."
"That still doesn't tell me what it does" John replies, exasperated.
"A gun, John" Sherlock answers.
"A what!?" John stares at Sherlock, remembering all the times when Mycroft would casually point at this or that with his umbrella.
"Don't make me repeat myself John, you know I don't like to, it's a waste of time" Sherlock answers.
"But that's just- he's surrounded by his people all the time! Who is going to manage to get close enough and be a big enough threat for Mycroft to shoot?"
"You'd be surprised, he's used his umbrella on several occasions."
"Like when?"
Sherlock sighs and finally closes the laptop "One of the times that I recall happened soon after Mycroft got the umbrella."
"It wasn't actually raining that particular Saturday morning. Back then well, you know Lestrade's excuse for looting my flat so you can guess. Mycroft had come to retrieve me from my latest caper in the northern part of London. He managed to come in to get me unmolested and we returned outside shortly. I remarked at him having an umbrella as there was no danger of having a storm for the next 16 hours."
"Mycroft only said his custom order was in and I should get used to the umbrella because it wasn't going anywhere. For the duration of our trip I puzzled out the nature of his umbrella. Although I pride myself on my skills of deduction, without getting my hands on the umbrella itself I could only limit the possibilities to three, maybe four. Mycroft, being the annoyance that he is, refused to let go of his umbrella so I could not get my hands on it. When we finally arrived at our stop and exited the car there was an armed man waiting for us. Ordinary people wouldn't have noticed that he was armed because his weapon was concealed but I quickly noted it."
"None of Mycroft's men seemed to be around, we were almost completely alone on the side of the street. The man remarked that 'this is for my sister' and pulled his gun as Mycroft flipped his umbrella around."
John waits for Sherlock to continue, huffing when he doesn't "And then what?"
"I shot him" John nearly jumps when Mycroft answers, when did he come back in anyways. His car seemed to have reappeared on the street below though John is sure it wasn't there a moment ago. "Honestly, must you reveal all the details about my security measures" Mycroft continues, focusing his ire on Sherlock.
"Why did you come back" Sherlock acts as though Mycroft hadn't spoken at all. The elder Holmes sighs and drops a file on the table.
"Some pictures that I have only just received involving the matter I want you two to investigate. I'll take my leave now and I imagine you'll hear from me in a few hours for a progress report." Mycroft turns to leave and John decides it's his last chance to ask.
"So you've really got a gun built into that umbrella?" John inquires.
"It seems your credit with dear John here has waned" Mycroft idly comments before turning and hooking the handle of the umbrella just above his elbow, holding the tarp material in his hand and flicking his wrist. A loud bang similar to a gunshot goes off and John turns, noticing that the smiley face Sherlock had shot into the wall long ago now has a nose.
"It's fine just the way it was!" Sherlock practically whines.
"Good day" Mycroft comments and turns the umbrella so the handle is back in his hand before heading down the stairs. Soon after Ms. Hudson comes up, an air about her that tells John the lady has just had a fright.
"John Watson what did I tell you about keeping your gun away from Sherlock!?"