The brilliant Idris Elba is back as the conflicted, perpetually tormented and fatigued detective chief inspector John Luther, the smart British cop who obsessively tracks criminals, sometimes without regard to proper procedure.

"Luther" returns next week as a third miniseries, this one four hours long and airing on consecutive nights Sept. 3-6 on BBC America.

The intense crime-solver is not only working two cases simultaneously, but he's battling a former cop hell-bent on taking him down for his unorthodox-to-illegal methods.

"If he breaks the law, I want his head on a stick," says his nemesis, George Stark.

Luther is also finding romance, an aspect of the story-telling that has been in short supply until now -- and it renders him slightly more talkative and a tad more revealing. Sienna Guillory ("Resident Evil," "Love Actually") plays Mary Day, a new love interest.

In addition, he's still grappling with his feelings for one Alice Morgan ( Ruth Wilson reprising that great character), a canny psycho-killer who got to him previously. She's cleverly reintroduced.

In the past short-run series, the tone has been gritty, intellectually satisfying and emotionally wrenching. This time around, a notable shift takes viewers into darker territory -- not just darker but manipulatively scarier with scream-inducing surprises that take their cues from horror flicks. Fans of detective fiction who liked "Luther" as a puzzle should prepare to be nudged over the line into horror territory. It's a leap some will decline to make.

There seems to have been a conscious decision to add a dose of not just violence but horrific suspense and shocking violence. The first hour in particular feels like a disappointing departure.

The character remains the same, even if he encounters accentuated gore and mental illness in the criminals.

Picture shows: DCI John Luther (IDRIS ELBA)
Picture shows: DCI John Luther (IDRIS ELBA) (Robert Viglasky)

He even grows a bit. The thing about love, he tells Stark, is it can "bring out the best in you but also the worst ... all your fears, rage, self-doubt." Of course he's wise when giving advice to others on the subject of love but not so clear-eyed about his own emotional vulnerability.

The third hour dips into the muddy area of vigilante justice and crowd-sourced decisions on guilt or innocence in the age of social media. Luther says he knows nothing about digital technology -- and that's a relief. He's best when pounding the pavement, roughing up a suspect or pacing before a wall of thumb-tacked evidence. Elba dominates every scene, his broad shoulders overwhelming the screen.

He's one genius crime-fighter we don't want to watch sitting behind a computer.