2) How Much Of This Episode Had Been Pre-Planned?
The revelations of “The Final Problem” turn our view of Sherlock’s character on its head. Previously, we’d been led to believe that his big childhood tragedy was the loss of his dog Redbeard – but it’s here revealed that this was his young mind covering up the fact that his best friend Victor was murdered at five years old. It’s a shocking twist – but we have to wonder how much of it had been in the works and how much developed as it went along?
Certainly writers Steven Moffat and Mark Gatiss knew they were going to introduce a third Holmes sibling by the end of season 3 – as Mycroft oft-handedly mentions “the other one” in that season’s finale “His Last Vow.” However, there isn’t anything in that season to suggest that Redbeard is anything other than a dog, or that Sherlock has gaps in his memory, so that seems to have popped into Moffat and Gatiss’ heads later on.
One small moment from way back in 2012’s “A Scandal in Belgravia” does suggest there was at least a vague plan all along. That’s because at one point, Mycroft mentions to John that Sherlock used to want to be a pirate. The camera then stays on him as his expression slips into sorrow. This can only be a reference to the fact that something terrible happened in Sherlock’s childhood.