Mycroft had always known that a truly powerful man needed to keep his distance from all other men. A touch of mystery, some slight eccentricity; a visible statement to all underlings, enemies and friends that they did not, could not, and would never understand this man.
An umbrella. At first it was practical. After all, London in winter was notoriously predictable. Carrying an umbrella in summer also had many advantages, not least of which was the aura of infallibility it created when it rained.
Finally, of course, there was the real reason for the umbrella, which only Sherlock and Anthea knew. Mycroft was always prepared for unexpected opportunities. He wasn't addicted, not by any means. Sherlock had the addictive personality, not Mycroft.
Sherlock, naturally, would insist on needling him about it in public with pointed comments about eating and his weight. As if Mycroft would care what people thought about something as superficial as body image! No, Mycroft's sole concern was that Sherlock would reveal his hidden foible and expose him to ridicule.
Then came the day that Greg was in the car with him when an irresistible opportunity presented itself. Mycroft called for the car to stop, and the two of them stood on the side of the road together.
Finally, Greg understood.
"You use the umbrella for picking blackberries?"
A/N: This piece was born when I was unexpectedly given the opportunity to pick blackberries. I got scratches and prickles all over my hands and I spent the entire time wishing I had something long with a hook on the end to reach up for the best branches, and thinking "dammit, Mycroft would never have been unprepared..."