Because, however you dress it up, a police procedural is a police procedural. The events of previous "Luther" outings drive a major story line - it helps to know that people around Luther have a way of dying and that he's had an odd relationship with a picturesque psychopath named Alice (Ruth Wilson) - but they don't make the cases Luther's working on now any less urgent.
And it's the cases, particularly the one introduced in the very first scene tonight, that feel as if they've been ripped from our very nightmares.
Or mine, anyway.
The presentation may be Hitchcockian at times, but there is nothing fun or arch or cartoonish or even particularly original in the violence that permeates "Luther." It is, quite simply, terrifying, and we are meant to take it as seriously as Luther himself does.
Serious doesn't actually even begin to describe Luther, who wears the weight of all that past and present violence the way he does his overcoat and whose infrequent smiles are therefore all the more devastating.
It doesn't hurt "Luther" that most police officers in Britain don't carry firearms and that the title character and his comrades share a vulnerability with those they protect that a fictional U.S. cop doesn't necessarily project (although being armed doesn't, of course, always prevent real-life officers from being killed or injured on the job).
We're used to British detectives who live more on their wits than their ability to bring deadly force, but Elba's Luther is both a physical and an intellectual presence. So it's all the more startling to see him in situations where he's unquestionably in danger.
And startling to me that a cop show can still have me checking for bogeymen before I switch off the lights.
Scheduling reminder: To avoid interfering with this week's episode of that other splendid whodunit, "Broadchurch," BBC America will be showing "Luther" at 9, not 10, on Wednesday.
Welcome back, Jon
Also back Tuesday: Jon Stewart, who took the summer off from "The Daily Show" (11 p.m., Comedy Central) to direct a movie and left behind John Oliver.
Kudos to Stewart for making a move outside his comfort zone, and even more for having the guts to leave behind a strong replacement.
Stewart's delivery - like his teeth - may be more telegenic, but Oliver proved to be a terrific jolt for "The Daily Show," with commentary that was often even more pointed than his boss'.
It probably helps to be saying tough things with a British accent, but it takes more than an accent to be smart and funny (see Morgan, Piers) and Oliver delivered both night after night.
On Twitter: @elgray