In which the most important character development of Sherlock Holmes is when he chooses to focus on the life that needed saving, instead of the satisfaction of an answer to the puzzle.
As demonstrated by the earlier phonecall from Mycroft, the Holmes brothers have always distanced themselves from human interaction and getting involved. The utmost importance always lied in objectivity— always needing there to be answer. Mycroft dominating Sherlock’s head in this scene signified this second nature of cold calculation and the reflexive search for who did it. Thus, while Mycroft was at the helm, all Sherlock could see was “who is the Mayfly Man?”.
We’ve seen this before in The Study in Pink and The Great Game, where Sherlock only cared about who the mastermind was, never minding the lives that were lost along the way.
Not this time.
At the height of his deductions, he forcibly shuts Mycroft off along with his obsessive compulsive need to know who did it saying “Not you—you.” And he then points to John.
And this is where the most powerful character development occurs because it is immensely difficult for Sherlock to consciously put aside the obsession over a culprit (evident from the fact that he had to slap his own face) and yet here, we witness him recognize that John is always the one to put lives first above all else, and for once, he will too. He turns away from who did it to who can we save and what Sherlock sees then changes to target.
He chooses John to rule his head saying that John keeps him right, and more importantly, to not
solve the murder; save the life. For once, in all his cases, Sherlock consciously realizes that there are more important things than deducing who the culprit is; it is the people they can save. For once, Sherlock cares.And if that isn’t A+ character development that was so humanly natural it slipped by unnoticed, then I don’t know what is.
[gif credit to ughbenedict]