Sherlock co-creator Steven Moffat has answered some questions on the upcoming 4th season, which will follow a completed special.
He told Entertainment Weekly Season 4 will be about “consequences”:
What distinguishes season 4 from previous years?
We haven’t started writing it yet, so it’s early. The first series was all about the beginning of their friendship. Second about the formative stages, the love and fear and loss and all that. The third was good days, me and my pal and my pal’s wife. Those are golden days. The missing element in a lot of Sherlock Holmes adaptations is allowing it to be funny. There’s a lot of humor in Sherlock Holmes, and it’s ignored in a lot of adaptations. [Season 4] is going to be… I suppose you’d say… consequences. It’s consequences. Chickens come to roost. It’s dark in some ways—obviously it’s great fun and a Sherlock Holmes romp and all that—but there’s a sense of… things… coming back to bite you. It’s not a safe, sensible way to live. It’s hilarious and exhilarating some days, but some days it’s going to be bloody frightening.
Is it more serialized than previous seasons?
Probably. A lot of serialization is latent, isn’t it? It’s hidden. Series 3 doesn’t look very serialized, but you look back at how much we’re setting up Mary [Amanda Abbington] to be who she turns out to be. It will be three stand-alone films, 90 minutes each, and an ongoing mystery, as there sort of always is.
How will fans feel after watching it?
Hmmm… desperate for series 5. We’re certainly going to put them through the mill. It’s going to be more of an emotional upheaval. Hopefully enjoyable and fun, all the things Sherlock must always be. It will be tough at times. Maybe that’s the word? A tougher series.
You can read more on the Q&A, including a question on a Doctor Who / Sherlock crossover here.