Season 4 will see our two detectives taking on a new villain (Toby Jones as iconic Holmes villain Culverton Smith), while John tries to take on the challenge of being a new dad.
With Sherlock season 4's final episode titled "The Final Problem" fans are wondering if this is truly the ending of the show. Co-creator Mark Gatiss acknolweges that this indeed could be the end, stating that, " It’s just genuinely difficult to schedule everyone’s diaries. It was a nightmare to schedule this season… and that’s not going to go away. I mean, the success of Doctor Strange is not going to make Benedict short of work.”
However, Gatiss also revealed to TV Line that if it were up to him, he would like to continue the series longer, in order to reach a very specific Easter egg-style ending:
"Right at the beginning, we said, wouldn’t it be fun — because we start with the first meeting, which is very rarely dramatized — if we actually ended up with them at the same age as Basil Rathbone and Nigel Bruce? That would be a really interesting place to be with Benedict and Martin, having started so early in their careers as young men."
For reference: Rathbone and Bruce were Holmes and Watson in 14 films; Benedict Cumberbatch and Martin Freeman would need about another 14 years of Sherlock under their respective belts to equal the Rathbone/Bruce run. At current pace, that's about three or four more season of the show.
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Sherlock Season 4 is set to debut on January 1, 2017.