A stench of sour milk pervades the flat, in which a neon yellow smiley face is daubed over old-fashioned flock wallpaper.
On the mantelpiece, a pile of letters is stabbed through with a penknife, and near the door there’s an African hunting spear in the umbrella stand.
Welcome to 221b Baker Street, the most famous address in London and home to Britain’s most famous detective, one Sherlock Holmes.
But we’re not in London. We’re in an enormous studio in Cardiff. And Sherlock, alias the very affable Benedict Cumberbatch, 35, is holding court alongside his sidekick Dr Watson, also known as Martin Freeman, 40.
They’re still reeling from the success of the first series which, thanks to modern technology, was pretty much instantaneous.
When the first episode, A Study In Pink, aired last July, Cumberbatch remembers sitting with creators Mark Gatiss and Steven Moffat, plus Moffat’s wife and producer Sue Vertue, in the Moffats’ garden.
“All the twittery stuff started to happen,” he says. “We were trending, which is apparently brilliant, and by the end of it I thought there would be people abseiling into the garden just to have a peek at us because this thing had exploded that night. It was thrilling.
“There was an amazing feeling of love for it. Of course, it had its detractors and it would be weird if it didn’t, but the feeling was one of great goodwill.”
The following day, Culture Secretary Jeremy Hunt namechecked Sherlock in a discussion at the House of Commons about the licence fee, saying Freeman and Cumberbatch “did a brilliant job”.
The series went on to be nominated for seven TV Baftas, winning three for best series, editing and best supporting actor for Freeman (“It was just a very nice cherry,” he says modestly), while Cumberbatch now has a whole army of online fans.
It’s also gone global, winning Emmy nominations and two very high-profile fans in directors Steven Spielberg, who cast Cumberbatch in his film version of War Horse, and Peter Jackson, who shifted filming on The Hobbit in New Zealand so that Freeman could make more Sherlock.
“He said, ’We want this to work’, so he put the film in chunks so that I could do this,” says Freeman, his cheeky smile giving way to a look of astonishment.
Despite the high level of expectation that will greet the new adaptations, kicking off on New Year’s Day, the team are showing no fear.
“Why wait?” says Moffat, confidently. “It doesn’t get better than these stories.”
A Scandal In Belgravia, based on Conan Doyle’s first short story A Scandal In Bohemia, opens where fans left their heroic duo – at a swimming pool, with Watson wrapped in a belt of explosives and Moriarty’s (Andrew Scott) men training guns on them.
After escaping the deadly pickle, the pair are then engaged by Sherlock’s brother Mycroft (Gatiss) to procure some rather compromising images from high-class escort Irene Adler (Lara Pulver) – a lady who fans of the original stories will know Sherlock finds hard to resist.
“The more I think about it, the more I start going, ’Oh s**t, yes we are doing three really huge stories’,” says Cumberbatch.
“But while I’m responsible for giving my Holmes, it’s a huge collaborative effort. It as much levels the responsibility at the script writers, the director and everybody else acting in it.”
Gatiss and Moffat, self-confessed “proper geeky Sherlock fans”, came up with the idea for the adaptations while working on Doctor Who.
They were chuffed to be given the thumbs-up from the Sherlock Holmes Society, with one member telling Gatiss it was “the best screen depiction he’d ever seen”.
The relationship between the calculating genius Holmes and the reassuringly more human Watson is central to the series – and it’s mirrored by the off-screen friendship of Freeman and Cumberbatch, who met for the first time on set.
“We rub along pretty well, me and Ben,” says Freeman.
“We have our ups and downs,” adds Cumberbatch, laughing. “Hopefully I’m less of a pain in the arse than Holmes. But we get on very well, we’re not living in the same flat or anything, that would be weird, but I adore him and his family, and he’s a rock of support.”
Apart from the double act, it’s Holmes’s deductions that really capture the audience’s imagination.
“I think people love the idea of someone who’s that hard-nosed and purposeful,” says Cumberbatch.
“A man who’s slightly sociopathic, who has the ability to read the world as a continual series of linking adventures and potential outcomes.”
The actor also admits he enjoys the chance to be devastatingly rude. “Because you can’t be in real life,” he explains.
“That’s one of the thrills of watching him. We love the outsider who kicks against bureaucracy, is impatient with mediocrity and strives for a level of brilliance which is achievable through hard work.
“He’s not a superhero, he makes superhuman effort, but it costs him” – a hint that in this series Holmes could be heading for a fall as his list of enemies grows longer.
When the second series started shooting, the actor admits it took him a while to find his character again. “I felt like I was impersonating something I’d seen on telly last year. It felt a bit odd that it now had this life outside what we’d done in front of a camera.”
He also found it a struggle to match the detective’s frenetic pace. “Sometimes there are days when I have to neck a couple of espressos, but others it has to be more of a maintained energy, so a coffee high is a terrible thing. It’s great for one take but not if you fluff a line, which I’m bound to do.
“I’m very lazy in comparison to Holmes and I operate at a far lower speed. His kind of neurotic, thin, high-end pitch is not me.”
Freeman is already looking forward to a third series. “It’s the first thing I’ve done in a while that I’ve thought, ’I’d like to do more of this’. This has legs because the people who put it together know the original stories inside out.
“I’d be the first to say, ’Let’s just stop now’, because then no one can take it away from you, but I honestly think and hope that it goes on for as long as it’s right to.”
EXTRA TIME – THE ORIGINAL STORIES
These three Victorian tales from Sir Arthur Conan Doyle have inspired the three new episodes of Sherlock.
:: A SCANDAL IN BOHEMIA
In the first Sherlock Holmes story ever published, the crown prince of Bohemia calls on the detective to obtain an incriminating photograph of himself and Irene Adler (an American opera singer) so that his family will allow his upcoming wedding to take place. Adler would go on to appear in further stories.
:: THE HOUND OF THE BASKERVILLES
The third of Conan Doyle’s four Holmes novels, and arguably the most famous. An aristocratic family in Devon is plagued by a supernatural, murderous hound after a descendant was killed pursuing a young girl across the moors. Holmes’s help is enlisted when the death of Charles Baskerville rekindles fears that the hound remains at large.
:: THE FINAL PROBLEM
Holmes’s ’final’ adventure begins with the introduction of his nemesis Professor Moriarty. A plot weaved by Holmes to bring Moriarty down leads to a climactic meeting at the Reichenbach Falls in Switzerland, from which neither return. Public uproar forced Conan Doyle to resurrect Holmes a decade later in The Adventure Of The Empty House.
:: Sherlock starts on BBC One on New Year’s Day