The BBC show’s writer, Stephen Moffat, has previously hinted that the third Holmes sibling might appear. In the final episode of series three, His Last Vow, character Mycroft, played by Gatiss, said: “I’m not given to outbursts of brotherly compassion… You know what happened to the other one.”Previously released pictures also show Watson and his wife Mary carrying their baby, with Sherlock looking distinctly unimpressed at the new addition. The first episode will be written by Mark Gatiss, who also stars in the show, and will see Sherlock awaiting the return of his nemesis Moriarty.“One mysterious case in particular baffles Scotland Yard – but Sherlock is more interested in a seemingly trivial detail,” information about the programme states.“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…” Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings. Baroness Thatcher admires a statue of herself at the Guildhall Art Gallery The dark image show Benedict Cumberbatch as Sherlock Holmes The second episode of the series will be entitled The Lying Detective, assumed by fans to be a new version of The Adventure of the Dying Detective.The series, due to begin on New Year’s Day and one of the most hotly-anticipated shows of the season, will see Toby Jones join the cast as Culverton Smith, the dastardly villain of the second episode.Previous clues have hinted at the introduction of a second new character, Sherrindord, known to Sherlock aficionados as the detective’s older brother. Benedict Cumberbatch as Sherlock, with hound The teasing glimpse of the plot has now been released by the BBC, along with a new image of the show which will raise more questions than it answers.The photograph, starring Sherlock and Watson, sees water rising around their ankles and a series of strange items floating around them.They include a music score entitled “Miss Me?”, a copy of Shakespeare’s Henry V, a teacup, a sequinned Persian-style shoe, a yellow face drawn on the mirror, and a violin.A model RNLI lifeboat is also perched on the shelf, indicating something of a water theme.As usual, the image is likely to spark a frenzy of fan speculation, with a moving version of the picture debuted on the BBC at 10pm on Wednesday. The Abominable Bride, from the last series of Sherlock Toby Jones has been confirmed for the new series The BBC has long endured accusations of being full of left-wing luvvies. And the team behind Sherlock appear determined to play up to that reputation, as they announce a new episode in which a mysterious stranger is smashing up images of the late Baroness Thatcher.A New Year episode of Sherlock, starring Benedict Cumberbatch and Martin Freeman, will see a plot unfold around the extraordinary vandalism of six art works depicting the former Prime Minister.Information about the mischievous show states: “Why is someone destroying images of the late Prime Minister Margaret Thatcher? Is there a madman on the loose?” The title of the first episode is The Six Thatchers, already widely tipped to be an updated version of Arthur Conan Doyle’s The Adventure of the Six Napoleons.That 1904 story saw Sherlock presented with a seemingly trivial case of smashed plaster busts of Napoleon, abandoned on the scene in various shops and homes with nothing apparently being stolen.The 2016 update now seems likely to involve six similar busts of Lady Thatcher.For admirers of Lady Thatcher, the show could be seen as a case of art imiating life. In 2002, a real statue of the former Prime Minister worth £150,000 was decapitated by a protestor at the Guildhall Art Gallery, London.