There was a period in the mid-’90s when I asked an English acquaintance why his country’s TV shows were so much better than ours. He laughed and said that I thought that because only the very best stuff was being sent across the pond, that very few Brit series were up to the standards of a “Prime Suspect,” and that if I spent enough time watching the shows he did, I’d find it to be every bit as mediocre and formulaic as most of American TV.

I thought about that conversation quite a bit as I got deeper and deeper into Luther,” a six-part cop drama that BBC America is bringing over here starting Sunday night at 10. Were it one of only two or three Brit crime shows I’d ever seen, I imagine I’d have been floored throughout. But I’ve seen enough other shows just like it that I had to leave the novelty aside and judge it on its own merits. And those merits include two fantastic lead performances by Idris Elba and Ruth Wilson, but also some muddled overall storytelling that left me scratching my head by the time we got to the final act.

Elba, who will forever be identified by the small but passionate audience of “The Wire” as upwardly-mobile drug dealer Stringer Bell, is John Luther, a London-based detective who’s brilliant but also unhinged. We’re introduced to him as he’s closing in on a child abductor whose latest victim may still be alive, and the methods he uses to locate her are more Jack Bauer than Lenny Briscoe. He’s suspended, investigated and reinstated, and everyone - his boss Rose (Saskia Reeves), best friend Ian (Steven Mackintosh) and estranged wife Zoe (Indira Varma) - views him as a ticking time bomb. He’s too good at catching bad guys to be left on the sideline, but too much like them for anyone to totally trust.

The notion of the hero who learns to think like a killer in order to catch them is a familiar one by this point, and practically its own sub-genre on British TV, with other notable examples including “Cracker” and “Touching Evil.” (Both had interesting but unsuccessful adaptations on American TV.) So where “Luther” has to stand out is with its performances and its storytelling.

On the former, it succeeds wonderfully. Elba is tall and striking and has a singular presence (in one of the later episodes, another character notes the futility of Luther trying to wear a disguise), and yet he ably transforms himself from his usual smooth screen persona into this stooped, bow-legged, volatile wreck of a man. It’s a riveting performance, and matched by that of Ruth Wilson as Alice Morgan, a killer so clever and crazy that she spends the six episodes veering wildly between being Luther’s arch-nemesis and closest ally. Where Luther has the clearly explosive temper, Alice’s own insanity manifests more unpredictably, and Wilson is strange and compelling throughout.

The cat-and-mouse games played between the two are the highlight of “Luther,” but the deeper we get into the series, the less we get of it. Several episodes in the middle are focused almost entirely on Luther’s hunt for other serial killers - and are largely indistinguishable from your typical hour of “Criminal Minds” - and then the larger arc takes a bizarre and unconvincing left turn in the final two hours.

So long as Elba’s on the screen, I’m interested, and even more when he and Wilson are sharing it. But ultimately, “Luther” turned out to be more average than I thought at first, regardless of its country of origin.

(A couple of notes before the comments. First, please keep in mind that the No Spoiler policy around here means that if something hasn't yet aired in America, it's a spoiler. I'm sure many of you have already seen all six episodes of "Luther," but I don't want to see them discussed in anything but the most broad of terms. Okay? Second, because of that time-shifted audience issue - and because, frankly, I didn't love it as much in the end as I had hoped - I won't be doing weekly posts on this. Probably something quick after Sunday's premiere (my favorite episode) and maybe another one after the finale.) 

Alan Sepinwall may be reached at sepinwall@hitfix.com