BBC4 should make a documentary about how cable TV revolutionised American drama. "The HBO Story", or whatever they called it, would tell how, suddenly no longer beholden to advertisers, US television was able to transform itself from the bland and infantile into the sophisticated and adult; how we are in the midst of a modern golden age of comedy and drama that includes (to name but a few) The Sopranos, Sex and the City, Entourage, The Larry Sanders Show, Curb Your Enthusiasm, The Wire, Six Feet Under and Dexter.
Those last two shows have made a reluctant star of 37-year-old actor Michael C Hall, who likes to operate in (his conversation is peppered with the expression) "grey areas". First seen by viewers in this country as repressed gay mortician David Fisher in Six Feet Under, Michael C Hall (the C stands for Carlisle) has cemented his reputation for complex and morally ambiguous roles with Dexter, in which he plays a charming sociopath who has the perfect cover of working as a blood-splatter specialist for the Miami-Dade police department. Unable to form much in the way of normal human relationships, Dexter satisfies his inner urges by killing the criminals who have eluded justice. He's a one-man capital punishment roadshow, and we have been asked to identify with him.
"I appreciate that the show operates in a grey area and creates a sense of ambiguity in the viewer," Hall says, "I'd like to think that maybe the show takes a bit more responsibility than some do in terms of what it's portraying."
The American pressure group, Parents Television Council, isn't so sure. Its president, Timothy Winter, articulated the misgivings of many when he declared: "The biggest problem with the series is something that no amount of editing can get around: the series compels viewers to empathise with a serial killer, to root for him to prevail, to hope he doesn't get discovered."
Just last month Dexter's producers faced the nightmare of what appears to have been a copycat killing after a 29-year-old film-maker from Edmonton in Canada, Mark Twitchell, was arrested for a murder that suggested life was imitating Dexter. "I don't think the show in any way advocates being a serial murderer," Hall tells me. "If I did I would have a problem, but it's a meditation on the nature of morality rather than a celebration of the serial-killer lifestyle."
He rightly adds that the show is also very funny, from the witty credit sequence in which Dexter's morning routine – shaving, squeezing orange juice, making coffee – is made to look like the most graphic of murder scenes. "It's a constant challenge to discover and maintain the right tone," he says. "There's something quite serious going on but at the same time a levity must be achieved otherwise it's not going to be palatable."
Season one of Dexter, picked up for a wider audience in this country by ITV1, introduced Dexter's back-story; how he was traumatically orphaned at the age of three and adopted by a Miami cop who recognised Dexter's sociopathy and taught him to behave normally and channel his murderous impulses in a "socially useful" direction. This included the hunt for a mass murderer known as "The Ice-Truck Killer", who turned out to be Dexter's long-lost brother, Brian, fiancé of Dexter's adoptive sister Debra. It all ended with Dexter killing Brian to save Debra, and faking the fratricide to look like suicide. Quite a Freudian stew. Where can the show go from there? Fans can find out on 8 January, as the second series begins on ITV1.
"The arc of the second season, in part at least, will be one of rehabilitation and healing," says Hall, who speaks slowly and deliberately. Playing back the tape later, it was like listening to Dexter's deadpan narration that punctuates the show. "Dexter will come to experience himself in ways that could be described as more human, but an inherent sociopathy will remain. Otherwise, well, it would be nice to know that he lived happily ever after, but no one would want to watch it."
There is no doubt that people are watching and appreciating Dexter. The show has been picked up all over the world. The opening season was nominated for an Emmy in 2006 and Hall was nominated for a Golden Globe (as he was for Six Feet Under). Did the success come as a surprise? "I suppose I was somewhat surprised at the breadth of the show's appeal," he says. "Some of it is quite realistic but there are fantastical elements and I always believed that walking that line would be the key to its success."
One of those fantastical elements is the way in which Dexter incapacitates his victims, with a syringe to the neck. "Technically it's a horse tranquiliser," chuckles Hall. "There's an example of the show's comic-book fantasy – we are asked to accept that as soon as someone is jabbed they are incapacitated for a while and then wake up and become fully aware."
Having butchered his way through Miami's lowlife in season one, the second series finds Dexter having lost his mojo. He can no longer dispatch his victims – he can't, as Dexter puts it, "close the deal". "It's the first hiccup he's ever experienced," says Hall, who equates Dexter's killings with a sublimated erotic urge. Unable to connect emotionally, he doesn't have sex with his girlfriend Rita. But all that is set to change as Dexter, in Hall's words, "experiences a sexual awakening".
Hall famously doesn't talk about his private life. The persistent rumour is that he's dating his Dexter co-star Jennifer Carpenter, who plays his sister Debra, but Hall resents any intrusion on such matters. "I'm not compelled to cultivate that sort of interest," he says. "I try not to pay too much attention to it. It's not like it curtails the sort of life I lead. I don't frequent the sort of spots that are frequented by the sort of people who are courting that kind of attention."
He's not living it up behind the VIP ropes at the Viper Room, in other words. And although Los Angeles is now home, Hall's early career was in New York, firstly off-Broadway and in various New York Shakespeare Festival productions, before being cast as the flamboyant MC in Sam Mendes's revival of Cabaret. "Everything I opened up for Cabaret," Hall has famously been quoted as saying, "I slammed shut for David [Fisher, his gay Republican undertaker in Six Feet Under]."
David Fisher and Dexter Morgan – two peachy if potentially risky roles. Showtime has recently green-lit two new series of Dexter that, along with five years of Six Feet Under, adds up to what Hall calls his "TV decade". It's a considerable investment in the dark side. "I suppose if presented with the prospect of an open-ended commitment to a character that might take me through years of material, I prefer to play one who has layers of complexity."
How does an actor play someone pretending to have emotions? "It's a mind-bender," says Hall. "I guess I'm an actor playing an actor. It frees you from a preoccupation with 'oh, was that real, did that feel authentic, because Dexter's not preoccupied with that – it's all a simulation."
Hall then confirms a story I read, that to get into character when he first started playing Dexter, he would stalk strangers pretending that they had committed some monstrous crime. "Hey, but we're talking about 45 minutes to an hour – it wasn't a long, drawn-out stalking; it was a good way to focus my mind on the guy."
Has he ever been stalked? Hasn't a show like Dexter inspired the scarier sort of fan? "None who has contacted me directly," he says with a tiny chuckle that might have emanated from Dexter himself. You can see why the crazies might have kept their distance.
'Dexter' is on ITVI on Thursday 8 January