Blood, sweater and fears: Behind the scenes on The Killing

Oh hell, it's not going to be easy organising a Saturday night social gathering between now and Christmas. Indeed, I already know one couple hosting a long-planned dinner party later this month who have had to restructure their evening around the television schedules – as strange as that may sound in this iPlayer age. And we're not talking the latter rounds of The X Factor or Strictly Come Dancing here, but a painstakingly slow subtitled drama called – in its native language – Forbrydelsen (The Crime), and featuring an unsmiling middle-aged woman in jeans and Faroese sweater, municipal Danish politics, dodgy removal men and Copenhagen skylines shot in a crepuscular November light. If, at the start of this year, you were trying to predict the most talked-about TV dramas of 2011, one of them would almost certainly not have been The Killing.

Showing in double-episode blocks, this saga about the real-time investigation of the rape and murder of a teenage girl quickly came to grip over half a million viewers – more than watch Mad Men, albeit a paltry five per cent of the audience for Downton Abbey. That five per cent were however highly vocal (especially in the media) and in the grip of a powerful obsession, and any latecomers attracted by their word-of-mouth praise were able to quickly catch up on BBC iPlayer. A cult was in the making.

And now, fellow devotees, it's back – and as gripping as ever I am relieved to say. But a really shocking plot development is not the fact that a woman has been horribly murdered in her home, dragged to a landmark Copenhagen park and tied to a post – although that is the attention-grabbing opening to The Killing II. Nor that the Danish government is struggling to pass new anti-terrorist legislation, although that is the backdrop to the 10-part sequel. The real gasper for fans of Sarah Lund will be that, two years on from the original, our heroine is working as a passport checker at some God-forsaken ferry terminal in the south of Denmark. It's like finding Inspector Morse on traffic duty or Sherlock Holmes consigned to delivering affidavits.

And what may rock some fans even deeper to the core is that Lund, played by 43-year-old Danish actress Sofie Grabol, has – ha, ha – changed her jumper. She now sports a red woolly sweater instead of the brown-on-white knitwear that saw her through the first series. Mind you, this iconic sweater business is wearing a bit thin, especially with Grabol, who was in London earlier this week for a gala preview screening at Bafta in London.

"Who cares?" she says. "Why don't people ask me about what happens to my character in the story? But every time that question. I love that sweater and I hate it... it's so strong that it's almost wearing me. Anyway, never give the audience what they want – so they chose this red jumper."

Grabol, a star in her native country for the past 25 years, has now found herself a British fan-base after playing a new sort of female protagonist – and is no sister of that other loner heroine of Nordic noir, Stieg Larrson's kick-arse, quasi-cyber-punk Lisbeth Salander. While Salander is the product of male fantasy – of how a woman (or, in this case, more of a girl) could act under pressure – Lund is a woman's idea of how a man would act. It's Grabol's idea of how a man would behave, starting by emulating her director's macho swagger. It was the only way she could find to play the part.

"I had always played very emotional characters," she says, "traditional feminine characters, and I wanted to play a person who's not able to communicate. I actually found it very, very difficult to play her." Not that, ultimately, Grabol sees Lund as a masculine character – "she's very feminine... she's just focused."

Probably her nearest antecedent has been Jane Tennison, Helen Mirren's chain-smoking DCI from the Prime Suspect series. But whereas Tennison had incipient alcoholism and sexist colleagues to define her, Lund's only dysfunction is her single-minded dedication to her job. It's a peach of a role in a peach of a drama, which makes it doubly surprising that Grabol had severe misgivings about making a sequel.

"No, I had to think about it," she says. "I've been an actor since I was 17 and it's so much in your bones as an actor that you get married to a project, and then you leave it and then you marry another project. The whole thought for me of going back to something that worked and ended beautifully, with no winners and all the question marks... Also maybe out of the fear of failing – I don't know – because you can't always live up to other people's expectations.

"However, Soren [chief writer Soren Sveistrup] has the same view on his own work – he never wants things to be easy – and I got a very strong sense that he had a good story and he would make sure that we wouldn't fall into a routine or fall asleep creatively."

A divorcée and the single-mother of two children, Grabol's breakthrough role was in Barndommens Gade (Early Spring) in 1986, a part she won despite coming from a non-theatrical background and never attended drama school – her mother having suggested that she audition. Mixing theatre (recently in a stage version of Ingmar Bergman's Fanny and Alexander), film (including the Oscar-winning Pelle the Conqueror) and TV (most prominently as Julie in the Emmy-winning Nikolaj og Julie, a sort of Danish Cold Feet), she has rarely been out of work since.

"I've always been very privileged in Denmark, moving freely between theatre and film and television," she says, "playing everything from Shakespeare and Strindberg and Ibsen to farce and comedy and modern plays, and actually in between every season of The Killing, I've done other things, so I don't feel stuck. I hope there is a life after Lund."

Lund of course wasn't the only strong female lead in The Killing. Ann Eleonora Jorgensen gave one of the most sustained and convincing portrayals of grief that I can remember seeing as Pernille Birk Larsen, the victim's mother, while of the male characters there were three dominant ones in the first series: Pernille's husband, Theis, the burly, woolly-hatted removal firm boss with a shady past (played with verbal economy by Bjarne Henriksen), Lars Mikkelsen as the ambitious and idealistic mayoral candidate Troels Hartmann, and Soren Malling as Lund's initially hostile police partner Jan Meyer. And of all the relationships in the series, I was unexpectedly most touched by the growing mutual regard between Lund and Meyer. The moment when she finally signalled her acceptance, by sharing a cigarette, brought an idiotic smile to my face, and this gesture was so much more brilliant than a plot development that the writers had in mind – to make Lund and Troels Hartmann have an affair. Fortunately, Grabol was having nothing of it. "I rushed into the writers' office and said: 'You are not doing that. It's a sell-out'," she has said. "I remember saying: 'I am Clint Eastwood! He doesn't have a girlfriend!'"

The cast's input is possible because of the highly unusual way that The Killing is constructed – one episode being filmed while Soren Sveistrup writes the next one. "That to me is an extremely challenging way of working and the reason – apart from Lund's fascinating character – why I stay on this project," says Grabol. "If we had gotten the 10 episodes in a nice pile on my table and I had read them all through, I think it would be very hard not to fix where I'm going... I'd settle on the decision, and it would be harder to move me from that. This way of working, of allowing the story to move freely, helps everyone else. The level of creative atmosphere on The Killing is very high."

Surprisingly – given that the biggest USP of the original series was the solving of one murder over 20 episodes – the writers had other killings up their sleeve in case their experiment didn't work and viewers grew restless. "Danish Broadcasting were very supportive," says executive producer Piv Bernth, "but when we pitched it to friends and colleagues they said, 'No, you can't do 20 hours on one murder, nobody's going to watch it.' It was a big gamble to do 20 hours on one killing."

In the event, the extra corpses weren't needed, and three-quarters of the Danish viewing public tuned into the final episode to find out who actually killed Nanna Birk Larsen. As so often with whodunits, much of the entertainment was provided by the red herrings and what is amazing is that in this digital age no one has given away the identity of the murderer in any of the newspaper articles, reviews and blogs that I have read. It's like The Mousetrap in that way – except unlike with Agatha Christie's West End warhorse, in this instance Wikipedia hasn't yet revealed the culprit.

Grabol has told the story of the letter she received during the Danish run of The Killing, from the relatives of a woman who was dying of cancer. The woman feared she wouldn't live long enough to find out who the killer was, and so Grabol wrote the name of the killer on a note and posted it to her. The woman read it and tore it into little pieces so her nurse couldn't find out who did it. "She died the following day," says the actress.

Fluid, intelligent storytelling, an interest in the victims of crime and characterisation way beyond the usual standards of the genre have all made The Killing a must-see treat, but in Britain the fascination has strayed beyond the usual parameters of drama and detection, to an appreciation of the chilly Copenhagen landscapes – the outside of the town hall and the police station, the woods near the airport – while the language itself became a source of fascination, all that "tak!" and "hej!" and "ses!". Something will definitely be lost if Denmark's public service broadcaster DR goes ahead with its idea of filming future series in both English and Danish.

Such "improvements" will thankfully come too late for The Killing II as well as the third instalment, which is currently filming in Copenhagen for transmission next autumn. There's the same musical score by Danish composer Frans Bak, but only four characters from the original The Killing remain – Lund herself, Lund's mother and son, and her boss, the looming and enigmatic Lennart Brix (Morten Suurballe). It's Brix who summons Lund from her exile at the ferry port, hoping that one of her informed hunches will help crack the stalled investigation into the woman who has been stabbed to death and tied to a post in Copenhagen's Memorial Park.

Once again filmed and set in the gloomy November light, the storyline travels along gratifyingly familiar tracks, with Lund having hunches that go against all the evidence (the tinkling piano music when she picks up on a clue is becoming something of a Killing trope) and a political backdrop, this time national not municipal. "Her problems this time must be some of the biggest institutions in Denmark, the military and the government," says Piv Bernth. "The task we set ourselves was to see how far into her darkness we could get."

Promising new characters in The Killing II include Thomas Buch (played by Nicolas Bro), the idealistic new Minister of Justice brought in to form a coalition that can pass the governing party's anti-terrorist legislation, and if you like to make comparisons to the original, Buch seems to be shaping up as the Troels Hartmann of this series. Then there is Jens, in prison for some as yet unspecified crime and hoping for parole, Islamic terrorists, right-wing minority parties and a shadowy group of ex-servicemen. Lund even leaves Denmark for Afghanistan, spaghetti Western territory in the south of Spain standing in for Helmand. "But It's not about Islamic terrorism," says Bernth."The tagline for the second season is 'How much do you bend democracy to defend it?'"

Grabol and Bernth won't reveal anything about The Killing III (well, it is November), except to say that this will definitely be the final outing for Sarah Lund ("it was originally conceived as a trilogy," says Bernth) and to disclose the fact that Lund will be buying her own house at last. This may seem like a mundane detail, but it was problematic as far as Lund's continuing mystique is concerned.

"We had this enormous problem," says Bernth. "How does she live? What does she have around her... apart from sweaters? We had to characterise her in some way. The production side was really wanting to show who she was (with her home) and everyone else was screaming, 'no, no, no... don't tell'." Adds Grabol: "Now we're filming the third season, it's becoming a struggle for me because on the one hand I want to get to know her better and on the other hand I don't. I like that even though she's a very strong character, she's also almost transparent somehow – there's so much you don't know about her. I like her mystery."

'The Killing II' starts on Saturday 19 November on BBC4

A SUBTITLED CRIME WAVE: FOUR NEW EURO SHOWS

The Bridge (BBC4)

How's this for an idea for a 10-part Danish/Swedish co-production? Have the initial murder victim discovered bang in the middle of the road link between the two countries. A bi-national police team is hurriedly put together in this show after the body of a woman is found halfway across the Oresund Bridge, between Copenhagen and Malmo, Sweden. Airing in 2012.

Sebastian Bergman (BBC4)

Rolf Lassgard (who plays Martin Beck in 'Beck' and Kurt Wallander in the Swedish version of 'Wallander') portrays yet another titular detective, a politically incorrect and grief-stricken Bergman, whose wife and daughter died in the 2004 Thailand tsunami. In the first of two 90-minute films, broadcasting next year, he helps solve the murder of a 15-year-old boy.

Braquo (FX)

The brutal offspring of 'Spiral' and 'The Shield', this French policier was the brainchild of actor, director and former flic Olivier Marchal, and focuses on a tightly knit and ruthless band of Parisian detectives under investigation for corruption. Starring Jean-Hugues Anglade from 'Betty Blue', the eight-parter began last Sunday on the digital channel.

Borgen (BBC4)

This new 10-parter from the makers of 'The Killing', screening next year, is not overtly a crime drama, but its story of a 40-year-old party leader (Sidse Babett Knudsen) who unexpectedly wins an election heads off down some distinctly murky byways. Bjarne Henriksen and Soren Malling from 'The Killing' feature, while 'Borgen' is currently being remade for US TV by NBC.