Aside from the cryptic clues handed out for the titles of the latest series of Sherlock, the key word for this fourth run of three episodes appears to be "darkness", as the show looks to raise the stakes for Benedict Cumberbatch, Martin Freeman and the rest of the characters. Check out the latest trailer below.
With Toby Jones as a big threat this year, and as show co-creator Mark Gatiss' Mycroft Holmes ominously warns, there are demons waiting to finally claim our hero. But there is some brightness in his world as Freeman's John Watson and wife Mary (Amanda Abbington) become parents.
The likes of Louise Brealey, Rupert Graves and Una Stubbs are all back, and the first of the new episodes, The Six Thatchers, will be with us on New Year's Day followed by The Lying Detective on 8 January and The Final Problem on 15 January.