This wasn't what he had anticipated.
When Detective Inspector Greg Lestrade, a man he had only ever heard of from Sherlock, showed in his place of work, Mycroft had expected something a little more important. Say, a threat to the world.
What he did not expect was a charming crooked grin, a sharp tongue, and an invitation to coffee.
"Make it tea," he says after a prolonged silence in which the DI's grin grew tighter and tighter "and we have a date. Out with you, now, I have work to do."