It's not a common occurrence for Mycroft Holmes to be rendered utterly speechless; thirty-six years of practice with his wilful little brother have prepared him for virtually anything, and yet he's left momentarily dumbfounded by Sherlock's latest request.
"Why on Earth would you want to adopt a child?" he enquires at length, because that's the most absurd thing he's heard in quite a long while.
"Not any child," his brother huffs impatiently. "Archie's different – I can't stand the thought of an intellect like his to go wasted."
"You're fond of him," he states, and it's one more deduction he clearly wasn't expecting. Sherlock glares at him, but that at least he knows how to deal with.
"Are you sure he doesn't have any surviving relatives?" he double-checks, though it won't be difficult for his PA to discover as much.
Sherlock shakes his head, and he sighs in surrender. He's going to pull some strings, argue with his brother until they reach a somewhat satisfactory agreement; but there is method in this madness, and he knows he can make it work.
Though in all fairness, it's probably Archie who's going to act as Sherlock's father instead of the other way round.