The Purloined Umbrella
Mycroft Holmes did not enjoy calling upon his younger sibling for assistance. He did, however, enjoy occasionally inconveniencing him, although he would never admit it should anyone enquire.
Sherlock Holmes did not enjoy interacting with his elder brother. He did, however, enjoy any opportunity to show him up, and he might admit as much should the right person ask the right question in the right way at the right time.
At a meeting on a gray London morning in Mycroft's office, Mycroft leapt straight to the point. (The only sort of leaping to which he was inclined.) "Grand-mère's umbrella has gone missing."
Sherlock nodded wisely. It had not gone missing from this office, nor from Mycroft's home, nor from one of his ubiquitous shiny black automobiles. That much was obvious.
"I need not remind you how important this is," Mycroft reminded him.
Sherlock returned to Baker Street where he found John Watson seated on the sofa and casually spinning an open umbrella before him.
"Mycroft is rarely so careless, particularly in public," said Sherlock. "Otherwise you wouldn't have managed it."
"You underestimate my sneakiness," replied John.
"Perhaps." Sherlock went to the kitchen where he'd left his latest experiment fermenting.
"How long do you plan to keep it?"
"Until he's learned his lesson. When I feel he has, we'll return Grand-mère's brolly."