The new Sherlock will be the darkest yet, co-creator Mark Gatiss has said.
Benedict Cumberbatch, 40, and Martin Freeman, 45, return for the next series of the BBC1 sleuth show - a three-part instalment - over the new year.
Mark, 50, who also plays Mycroft Holmes in the show, told Good Morning Britain: "It's hopefully the best three we've done.
"It's the darkest season. It's not a different show - it's still the combination of laughs and terror as it always is - but it has a darker edge to it and I think the cast have responded brilliantly to it."
He said actor Toby Jones's villain is "skin-crawlingly horrible" in the new series.
When Good Morning Britain host Kate Garraway jokingly asked if Mark had been a "bit lazy" because of the long gap between Sherlock series, he replied: "The Abominable Bride was on in January. It's not even a year!
"It always takes a long time, partly because it takes a lot to write and to make and also because Benedict and Martin are furiously busy."
Mark, who also writes Doctor Who, has previously hinted that he hopes to bring his dark comedy The League Of Gentlemen back to TV screens.
He denied reports that it would return with a Brexit twist, but confirmed: "We are hoping to. We have got a raft of anniversaries coming up that we're going to hook it on to.
"We're very excited. It's been 11 years since we did anything."