Finale to series 4 focuses on the third Holmes sibling, a sister called Eauros. Mycroft had her sent to a secure prison called Sherringford when. She was still a child after she ‘disposed’ of ‘redbeard’ and appeared to be plotting to kill Sherlock.
She then plays a game with Mycroft, Sherlock and John so they discover the truth about Redbeard, Sherlock’s childhood best friend Victor Trevor and the result of her meeting Morriarty (before the roof incident).
There isn’t very much of Molly, Mrs Hudson, Lestrade (although Sherlock dies call him Greg first time and unprompted in this episode), the Holmes parents, ghost Mary or baby Rosie, but it is nice that they all seem to be reasonablby ok in the end.
8/10