By Frazier Moore, Television Writer

NEW YORK (AP) --

Idris Elba has many reasons for why he keeps coming back to "Luther."

"It's unfinished business, it's fertile ground," he explains. "The character continues to challenge me."

Detective Chief Inspector John Luther also challenges his fans, who are sure to greet him warmly for this, his fourth run, in the two-hour special airing at 9 p.m. EST Thursday on BBC America.

As usual, "Luther" finds its hero possessed by a grisly murder case: a serial killer with a cannibalistic bent.

Meanwhile, he remains haunted by Alice Morgan, the tantalizing sociopath from Season 1 who escaped arrest by Luther but became his twisted confidante. Conspicuously missing, her whereabouts unclear, she remains very much on Luther's mind and a key part of this tale.

Elba calls the demons-beset Luther "one of the closest characters in terms of who I am." It's a surprising claim, since, during this recent interview, he seems light-hearted in stylish casual wear, a marked contrast to the glum expression and no-nonsense suit Luther wears.

"I don't feel like I have to throw on too much of a character to play John Luther," says Elba, attempting to explain himself. "We shoot in the area I grew up in (East London), and I really let the writer take me on the journey. It's the most naturalistic I can be in a role."

Even Luther's distinctive walk — a slouching swagger, hands jammed in his pockets, pushing forward with staunch intent — is comfortably derived from Elba's own gait: "I tore my left Achilles, which make my left leg sort of limp — or swag!"

A strapping, towering presence with leading-man looks, Elba nonetheless has been able to transform himself profoundly for his roles, such as the brutal leader of an African rebel army in his recent film "Beasts of No Nation," as Nelson Mandela in "Mandela: Long Walk to Freedom" and as Stringer Bell, the strictly business Baltimore drug lord, in the HBO series "The Wire."

No matter what his role, Elba is easy on the eyes.

Asked if he gets weary of his extreme handsomeness being the focus of media and fans alike, he adopts an almost sheepish expression while handing credit to the camera.

"Because I'm an actor, I've got that 'beauty light' on me," he insists. "In real life, it's not like that all the time. Some people go, 'He's nice, but he's not my sort of thing.'"

Acknowledging that too much attention to his looks could taint him as just another pretty face, he does allow that "it's a compliment and it's great, man. I could be described as 'aggressive,' or 'strong.' But 'sexy' works, too." And he laughs heartily.

At 43, Elba has been acting for more than 20 years, but says he's only recently understood what drives him as an actor: "I'm a person who absorbs a lot, takes in a lot of information every day, and with that comes an urge to let it go. As an actor I get to expel all that stuff by throwing it into my characters. Before I figured that out, I think I was motivated by the dream of being famous. But now I see that I do it because it's therapy, as well."

Next up is next summer's "Star Trek Beyond," which he shot last summer but can't talk about beyond confiding, "It was fun and different, especially after shooting 'Luther' last spring."

Even now, he isn't ready to be through with "Luther."

"The ultimate goal is to end up with him in a film," says Elba, who longs to turn him loose on a broader landscape than London.

"New York could be an amazing backdrop for John Luther," says Elba, motioning out the window of his Manhattan hotel suite. "I think that's what could be next for Luther," he says, pursing his lips for a muted explosion. "Movie time!"

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