Series four kicks off on New Year’s Day with the first of three brand new episodes.
Episode one is called The Six Thatchers, which suggests that it is based on Sir Arthur Conan Doyle's Sherlock Holmes story The Adventure of the Six Napoleons. We have done some sleuthing of our own about this particular story
Written by Mark Gatiss, the BBC has tonight released further clues about what it may be about.
A statement said: “Sherlock waits to see where Moriarty will make his posthumous move. One mysterious case in particular baffles Scotland Yard – but Sherlock is more interested in a seemingly trivial detail. Why is someone destroying images of the late Prime Minister Margaret Thatcher? Is there a madman on the loose? Or is there a much darker purpose at work? Something with its roots deep in Mary Watson's past…”
At the end of the last series, Sherlock resurfaced from a drug-induced reverie proclaiming "Moriarty is dead. More importantly, I know exactly what he's going to do next…"
That story – The Abominable Bride – revealed that the culprits were a group of women banding together to carry out the work of a fallen comrade. Will we be meeting more of Moriarty’s associates? You haven't got long to wait now...
Sherlock series four: The Six Thatchers is on New Year's Day, 1st January 2017, at 9pm on BBC1