Sherlock season 4: Everything we know so far from release date to plot as Benedict Cumberbatch starts filming

Fans have been promised 'laughter, tears, shocks, surprises and extraordinary cases'

Mark Gatiss holds up a clapperboard proclaiming the start of Sherlock series four filming (BBC)

Sherlock series four has finally started filming, with fans promised “ghosts of the past” and a baby when the long-awaited new episodes finally reach our living rooms.

Benedict Cumberbatch and Martin Freeman are returning, with showrunners Steven Moffat and Mark Gatiss hinting that the popular story is “about to reach its climax”.

Details remain frustratingly scarce and an air date is yet to be confirmed, but with the first titbits of information starting to eke out from BBC HQ, it’s time to round up everything we know so far:

The cast will be as stellar as always

With Cumberbatch and Freeman in high demand Hollywood-side, getting the cast together always proves a scheduling nightmare. But they are of course finally returning, alongside Amanda Abbington, Una Stubs, Rupert Graves, Jonathan Aris and Louise Brealey. Andrew Scott is obviously still a maybe as Moriarty and as of yet, no guest stars are known to have been booked. But there’s always the possibility of a surprise.

There will be a female director for the first time

Rachel Talalay, known for Doctor Who, The Wind in the Willows and The Flash, has 25-years experience under her belt and will direct the first new episode in the three-part series.

Moriarty looks set to make his presence felt

So no-one’s explicitly mentioned Moriarty, but the latest official hint of “ghosts of the past rising in the lives of Sherlock Holmes and John Watson” have made our ears prick up. These mystery “ghosts” will bring “adventure, romance and terror in their wake”, which sounds like a cocktail for excitement to us. Andrew Scott’s villain might have seemingly died last series, but that doesn't mean he couldn’t somehow reappear, either physically or supernaturally…

(BBC)

Doctor Watson and Mary are having a baby

Hurrah! There’s going to be a little’un in the world of Baker Street, with the BBC releasing a statement confirming the happy news. “Doctor Watson and his wife Mary prepare for their biggest ever challenge - becoming parents for the first time,” it read. Let’s hope daddyhood doesn’t disrupt everybody’s favourite bromance, mind.

There will be a “clear shift in tone” to darker things

Moffatt warned of a shake-up in tone at San Diego’s Comic Con last summer, when he told fans to expect “dark stuff coming...tragedy as well as adventure” with “a sense of things coming back to bite you”. Judging by Christmas special The Abominable Bride, there could be a more gothic edge to the new episodes. Ooh-er.

Mary might die but knowing Sherlock, might well not

Mary, played by Amanda Abbington, meets her maker in Arthur Conan Doyle’s original books. But whether Moffat and Gatiss will also give her the chop remains to be seen. They could well stray from the age-old plots, as they have done before, and throw an even bigger twist at us.

It’ll almost certainly launch on New Year’s Day

The BBC have reportedly said that it is a “near certainty” that series four will air on New Year’s Day, as has previously been the case. There seems little to suggest a chance of plan, giving that filming has only just begun and the episodes will need time to be edited. Such…a…long…wait.

But look, Cumberbatch has promised that the remaining months of unfed longing for new episodes will be “worth it”, so you’ll just have to take his word for it and sit tight in solidarity. Let the countdown continue…