‘River’ Perspective is everything for an unusual detective

Stellan Skarsgard stars in “River,” a six-part series first seen on BBC One and now on Netflix.

The cop-with-a-gimmick series and the cop-who-broods series are often different animals.

In the first, the lead character has some sort of investigatory superpower — Carrie Wells’ total recall in “Unforgettable,” for instance.

In the second, the lead character spends a lot of time brooding, often over a whiskey glass, about an ex-wife, estranged children, a botched case or all three.

“River,” a terrific six-part series first seen on BBC One that came to Netflix without much fanfare, re-energizes both those subgenres. The title character, John River, is a brooder with a superpower: He sees dead people.

That might sound hokey, but this series, created and written by Abi Morgan, is anything but that, growing deeper, darker and more intricate with each episode. (Check any “Sixth Sense”-related expectations at the door.)

The Swedish actor Stellan Skarsgard is superb as River, a British detective who as the series opens has recently seen his policing partner, Jackie Stevenson (Nicola Walker), murdered in a drive-by shooting. It’s not immediately clear that she is dead, though, because we see him chatting with her, something he does frequently as the show goes along.

“I’m not talking to myself,” he explains to a therapist in Episode 2. “There’s always someone there, someone I’m talking to.”

We, the viewers, often see that someone, whether it’s Stevenson, a victim from some other case or, more audaciously, Thomas Neill Cream (Eddie Marsan), a mass murderer from the 1800s. It’s not uncommon for River to converse with these invisible-to-everyone-else figures while other, living people are within earshot. If the series has a flaw, it’s that River’s erratic behavior makes it hard to believe he could stay on the job.

That said, he’s still a top-notch detective, coming up with insights others have missed thanks, partly, to his clarifying chats with the dead. River continues investigating the murder of his partner even though he has been ordered not to — he seems obsessed with her — and as he does, both he and we learn that she had her secrets. Morgan spools out the revelations slowly, cultivating an ominousness that infuses the entire series.

The show’s premise could easily have made this a silly enterprise, but with Skarsgard’s tight performance anchoring things, it instead is a first-rate psychological study. Sometimes River just seems crazy; at others, it seems possible he has ascended to a higher level of mental acuity, using the voices of the dead to tell his conscious mind things that he subconsciously knows.

Where police shows like “Columbo” and “Monk” have played with the question of whether a skilled crime solver is gifted or nuts, this one pushes that tension further, suggesting that the answer depends largely on perspective. Certainly River doesn’t think he’s insane.

A fine supporting cast also helps to sell the conceit. Adeel Akhtar does particularly nice, understated work as River’s new partner, who absorbs his eccentricities while patiently trying to steer him toward behavior that doesn’t shout, “I’ve lost my marbles.”