Sherlock co-creator Mark Gatiss promised RadioTimes that the fourth series will feature many of the familiar elements the BBC drama has become famous for. “You can always expect tragedy as well as adventure, that’s just how it goes," he said.
That could tie to Martin Freeman's earlier observation that Watson's wife Mary dies in Arthur Conan Doyle's stories. However, Gatiss noted that the television series isn't necessarily beholden to the source material.
"Just because it’s in the stories doesn’t mean it’ll happen in the series because there’s an awful lot of changes and an awful lot of places to go and things to do," he said. "It should be clear by now that while, of course, Doyle is our absolute God, we have gone quite a long way away as well – we’ve introduced Sherlock and Mycroft’s parents [for instance], I don’t think they’ve ever been seen in any adaptation – so there are lots of surprises to come."
Gatiss and co-creator Steven Moffat are working on the fourth series as well as a Christmas special.