I think this photo may make sense now.
The E string is broken.
There are 4 strings.
The 4 strings represent the 4 Holmes siblings; Sherlock, Mycroft, Sherrinford and now, Eurus.
The E string snapped.
Eurus probably had some sort of traumatizing thing happen to make her “snap”, turning her crazy, when she was a child.
When the E string snaps, it will effect the others because it has the
highest tension of the strings, and because of this it can change the tone of all the others.
So when Euros snapped, the rest of them, Mycroft, Sherlock, and Sherrinford, were changed badly because of an incident having to do with her.
It all makes sense now.
In episode one of this new series, written by Mark Gatiss, Sherlock waits to see where Moriarty will make his posthumous move.
One mysterious case in particular baffles Scotland Yard - but Sherlock is more interested in a seemingly-trivial detail. Why is someone destroying images of the late Prime Minister Margaret Thatcher? Is there a madman on the loose? Or is there a much darker purpose at work? Something with its roots deep in Mary Watson’s past…
Benedict Cumberbatch returns as Sherlock Holmes, with Martin Freeman as John Watson, Mark Gatiss as Mycroft, Rupert Graves as Inspector Lestrade, Una Stubbs as Mrs Hudson, Amanda Abbington as Mary Watson and Louise Brealey as Molly Hooper.