IT MAY be a show that unravels mysteries, but Lucy Liu's Dr Watson in new drama Elementary is certain to prove one of the series' biggest puzzles.

Eyebrows were raised by diehard fans when CBS's contemporary reboot of the much-loved Sherlock Holmes saw the drama transplanted to modern-day New York, the heavily-tattooed Jonny Lee Miller cast in the title role, and his sidekick, Dr Watson, transformed into a woman.

But with the show one week into its run in Australia, and already extended to a full season in the US (even having an episode programmed to directly follow this week's Super Bowl) the offbeat recipe seems to be working.

For Liu, playing the enigmatic, guarded Dr Joan Watson is a chance to put her action roles aside, and to take a more cerebral approach to acting.

It's a chance she's relishing, and a far cry from her roles on the big screen including Alex Munday in Charlie's Angels and the deadly O-Ren Ishii in Kill Bill Vol 1 and 2; or on the small screen as the vicious but hilarious Ling Woo on Ally McBeal, or, more recently, the hard-bitten and street-wise police officer Jessica Tang in television series Southland.

Her Watson is neither as physical nor as glamorous as we're used to seeing Liu, but she delights in just how well Watson can keep Sherlock Holmes off balance.

"This is definitely a very different kind of role for me, which is why I wanted it," Liu says. "There's not much action in this for Watson. It's mental gymnastics for her.

"It's definitely more cerebral. Action isn't subtle, and I'm enjoying the subtleties of Joan Watson for a change. This is a different kind of chaos."

In Elementary, Dr Watson meets Brit Sherlock Holmes in New York. He's as smart as a whip, eccentric, fresh out of rehab, and has just landed in Manhattan, where his rich father has assigned him a sober companion - Dr Watson.

Episode 1 revealed Liu's Watson is no shrinking sidekick to Miller's irrepressible, frenetic and constantly-in-motion Holmes.

Despite Holmes' insistence that Watson's expertise as an addiction specialist is not needed, he's quick to find she comes in handy as he resumes his work as a New York police consultant - albeit a very erratic and unconventional one.

And he discovers Watson is not so easy to dismiss.

"Joan Watson may be a sidekick, but there's no way she's there for laughs, or comic relief, or as a babysitter," Liu says.

While there was criticism of the move to make Dr Watson a woman in Elementary, Liu says it's given the character a new dimension.

"The narration of the original Sherlock Holmes is all through Watson's eyes, and having Watson as a woman gives it another edge in that Sherlock is always uncomfortable with women," she says.

"The fact that Watson is a woman who he has to be around all the time, for him, is kind of like him having to wear this uncomfortable, itchy sweater."

Holmes' growing realisation that he's going to have to take Watson seriously - and therefore he wants to know more about her - reveals Liu's Watson just may be the biggest mystery of all.

As a former surgeon it's obvious she has her own demons to battle - so far we know she was kicked out of medicine because a patient died on her watch, but it's clear there's a lot more to that story.

Liu is enjoying the slow unravelling of the mystery that is Dr Watson, as much as she enjoys Watson's growing appetite for solving crimes.

"We have progressed so much since the pilot. You really do see how she develops and how important she is in his life in the way she is able to deduce and figure out some of these crime scenes," Liu says.

"Her job is to help him through his emotional situations and difficulties, but he's fighting that every step of the way, so it's ironic that once she starts to notice things at crime scenes, he then has to respect her.

"We wanted to make sure he was up against someone that had that intelligence and grounding. He quickly finds that anything she brings to the plate is worthy."

Liu hints that Watson may have as many dark secrets as Holmes. "She has a complex back story," Liu laughs.

"They are two characters that are hard to know. You only get her story in dribs and drabs, because as a character, Watson distracts herself by helping others with problems, so she won't have to look at herself.

"He can be a really tough character and then he has moments when he's really open and vulnerable. That's when she really is able to reach out to him.

"They're both very messy people. They're both damaged. That's the beauty of them."

Flawed on-screen they may be, but when the cameras stop rolling, Liu and co-star Miller delight in a healthier relationship.

"Jonny is hilarious to work with. He has tonnes of jokes and a wicked sense of humour," Liu says.

"And what people might not know is he is also a really great cook. He has made some fantastic meals for me. He makes an absolute killer bolognese. He's very talented." For Liu, messy, flawed and mysterious is proving a successful recipe.

-- Elementary,

Ten, Sunday, 8.30pm

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-- HOLMES IS WHERE THE ART IS FOR SO MANY

LONG OUT OF COPYRIGHT, SHERLOCK HOLMES HAS BEEN PORTRAYED BY MORE ACTORS THAN ANY OTHER ON-SCREEN CHARACTER. HERE IS A SELECTION OF RECENT SHERLOCKS.

* (1984 to 1994)

Jeremy Brett has often been named as the definitive and most faithful screen portrayal of Holmes (at least until Benedict Cumberbatch). Brett played the detective as a neurotic but highly intellectual man in 41 episodes made for Granada Television. His ailing health is noticeable towards the end of the series, which ceased as a result of his death in 1995.

* (2002)

Australian Richard Roxburgh stepped into the role for BBC telemovie The Hound Of The Baskervilles, playing Holmes as a rather cold man who dabbles with drugs even while on a case. The hound was created using animatronics and computer effects. The movie was well received, despite taking a few liberties with the source material.

* (2004)

Rupert Everett took over the role for another BBC telemovie, this time an original story, Sherlock Holmes And The Case Of The Silk Stocking, set in a fog-plagued London. Everett's "elegant and decidedly decadent" portrayal was named the 12th Greatest Sherlock Holmes by The Daily Telegraph (UK).

* (2009 and 2011)

Robert Downey Jr's Holmes is rough and ready, intelligent and charming and rather handy with his fists. Unfortunately, neither of the Guy Ritchie-directed films, Sherlock Holmes or its sequel, A Game Of Shadows, rise to the level of Downey's and Jude Law's fine performances.

* (2010 to present)

Benedict Cumberbatch was born to play Holmes in the BBC's Sherlock. He is by turns aloof and arrogant, confident and funny, dashing and yet socially awkward. Writer Steven Moffat reinvents the original stories using modern technology and settings, bringing them bang up to date. A new series will be broadcast later this year.

- ANDREW FENTON