The King Must Thus Be Made
You cannot play at Chess if you are kind-hearted. - French Proverb
"…for life is a kind of Chess, in which we have often points to gain, and competitors or adversaries to contend with, and in which there is a vast variety of good and ill events, that are, in some degree, the effect of prudence, or the want of it." – Benjamin Franklin, The Morals of Chess 1786
Mycroft, of course, is the King. He is the most important piece in play, his value is infinite; but he is also physically the weakest, hence his need for protection from the rank and file. While he appears to only move at a slow pace, he is always leagues ahead of his opponents, his mind already planning the endgame. No matter what else is going on, the King must be protected. The King is the game.
Sherlock is the Queen. Moving dramatically across the board, seemingly free to move around, yet unaware of how his movements are controlled by the King. The name of this piece has changed over the long history of the game. One of the oldest names is vizer: the one who bears a burden. To listen to Sherlock is to hear him decry how he alone bears the burden of interacting with lesser pieces. The Queen Sacrifice is a move that can only be done once during the game and although it secretly pains the King to make this sacrifice, it will be done. The sacrifice signals the start of the endgame.
A piece of action for a man of action. John is the Bishop; able to keep up with the Queen, sometimes even getting ahead. This piece, too, has had different names over time: the madman, the messenger, the hunter, the shooter, the officer. John is all these things and more. In the hands of a less experienced player, the Bishop is often misused; in Mycoft's experienced hands, the power of the Bishop is explosive.
A Knight has to jump into the fray and mete out the King's justice and D.I. Lestrade is a true servant of the Crown. Knights are most useful when in the thick of things and excel at putting pressure on other pieces, especially enemy pawns. Some say that the Queen/Knight combination can be one of the strongest forces in the game, but in this game the Queen/Bishop pairing takes precedence.
Oftentimes unnoticed, unappreciated, and undervalued the Rook is a major piece on the board. Anthea works closely with the King as His Rook, His fortification, His connection to others, and when needed, His refuge against all who would assail His person. Winning the exchange for the King is what she lives for and she has placed the heads of many Bishops and Knights at His feet.
And then there are the Pawns, they are many in number and they are often sacrificed for the greater good. They live their lives en passant and move the game ever forward. Although it is almost impossible for them to understand the game they are playing, some Pawns are inextricably drawn towards the last rank where a battlefield promotion awaits. The King has his eye on one Pawn in particular; with the right guidance, Molly could be a Queen someday.