Some things are synonymous with New Year... midnight fireworks beside Big Ben, alcohol-fuelled renditions of Auld Lang Syne and, in recent years at least, a hotly anticipated new series of Sherlock.
fter whetting our appetites with a special at the start of this year (The Abominable Bride, the most-watched programme over the festive season, drawing 11.6 million viewers), the natio n's favourite deerstalker-wearer is back for a fourth instalment, kicking off with the first of three feature-length episodes on January 1.
After a trip to Victorian London for the last episode, Holmes (Benedict Cumberbatch) and sidekick John Watson (Martin Freeman) are back in the present day - and according to show creator Steven Moffat, it's the darkest series yet. "Without giving anything away, this is about as tough a journey as Sherlock goes on, and John actually," he says. "They kind of go to hell and back."
There's also a new baddie in the detective drama - "one of Sir Arthur Conan Doyle's finest villains" - played by Toby Jones.
"I hope Toby doesn't mind me saying, but he's a little man, and Benedict looms over him," says Moffat. "But he does somehow give an impression of a physical threat. There's something he can do to create extraordinary menace".
Viewers can expect plenty of light along with the shade though, as Cumberbatch reveals. "That is Sherlock's trademark," says the actor. "It's definitely not going to lose its humour. The relationships are more detailed and stronger and more explored than they've ever been, and there's great darkness in some of that, and also utter brilliance and light and love and goodness."
There's an important addition to the cast, too: Watson's baby daughter with his wife, Mary (played by Freeman's real-life partner, Amanda Abbington). Moffat jokes that the tot "must have superpowers by now". "Sherlock is still a scary man, John Watson's still an adrenalin junkie, Mary's still an ex-assassin - it's an extraordinary family group that this baby's being introduced to," he observes.
While the new arrival does help create "some of the most fun stuff and some of our most touching stuff", it doesn't mean the series will lose its action and edge.
Don't expect Sherlock to be changing many nappies for his friend. As co-creator Mark Gatiss, who also plays Holmes' brother Mycroft, notes, the sleuth "regards everything as a kind of specimen in a petri dish".
"Sherlock's not quite as in love with babies as I am, let's put it like that," adds Cumberbatch, who is expecting his second child with wife Sophie. "But he's got a deep affection for the child, because it belongs to two people he cares about."
Since Sherlock first aired in 2010, Cumberbatch has become a fully-fledged Hollywood star. In fact, the London-born actor went straight from wrapping superhero movie Doctor Strange to starting work on the detective drama the next day.
"I was finishing Doctor Strange in America going, 'Please! I haven't got time to learn this stuff, you've got to send it to me now!'" he says, referring to the latest round of Sherlock scripts. "Of course, I was a little bit excited, as well as learning my lines."
It took him a while to get back into Sherlock mode. "There are so many rugs being pulled under our feet so fast with the characters in this particular series, you don't have much time to re-establish what you already know of him before you're being challenged into something," Cumberbatch says.
As usual, there were plenty of Sherlock aficionados and 'Cumberbitches' (the term given to his dedicated band of fans) in attendance when filming went on location.
"By and large, they're an incredibly respectful crowd and they're a home crowd, and they really understand that they're essentially in our office for that moment," Cumberbatch adds. "It's sometimes a bit weird and confusing to know that you can't really be off, literally. If you trip, if you raise an eyebrow, it becomes an internet meme."
When Abbington and Freeman get their scripts, they read them together at home - and fill their two kids (Joe, 10 and eight-year-old Grace) in on some juicy plot details.
"I stupidly told my children what happens in this fourth series," Abbington confesses. "I say, 'Remember the swearing rule - you know when we swear at home, but we don't do it at school? Same thing applies to Sherlock. So swearing at home, Sherlock secrets at home'."
Freeman admits he finds the fast-paced scripts "very wordy".
"There's a lot in them that is not always understandable the first time you read them. Sometimes I don't fully understand until I've seen them broadcast ... 'Oh, that's what it meant!'
"A couple of times on this series, I've been walking around the kitchen an hour later, putting the kettle on in a daze of just having read a script that's so good I can't quite believe it," Freeman adds.
"Which is everything that you want in life as an actor. And hopefully, please God, it'll be everything the audience want."
Sherlock, BBC One, New Year's Day, 8.30pm