Warning: The following preview outlines general details for the premise of Counterpart, a new Starz sci-fi series debuting this weekend.

The “actor as multiple roles” genre has been done in a seemingly infinite amount of ways as of late: clones, siblings, whatever Cloud Atlas was. With Starz' new series Counterpart debuting this Sunday (8pm ET), the premise gets a slight twist. Beloved institution JK Simmons (everything from those insurance ads to Justice League and Whiplash) portrays mild-mannered office man Howard and alternate-universe spy bad-ass Howard Prime.

Confused? Luckily, audiences get the gist of this situation early in the series premiere: 30 years ago during the Cold War, scientists were experimenting when something went wrong, opening a passage between two seemingly distinct worlds. “Go through this door,” bossman Peter tells Howard, “and you’re in a world identical to ours.”

Sort of. Counterpart subscribes to the divergent timeline theory of sci-fi time, meaning Howard’s world and the Prime world have a shared history but then split and evolve based on the different happenings since. As just one small example, we learn both Howard and Howard Prime share a distaste for their brother-in-law and taste for striped ties, but Prime has become a pseudo-bounty hunter while regular Howard works a mostly administrative job within the same organization (Prime also deals with high cholesterol).

Within this slightly altered world, Counterpart has a more LeCarre-ish story to tell. Howard works at a secretive government agency in Berlin called the Office of Interchange, doing, well, he doesn’t really know what the OOI does initially. No one in the "normal" or "regular" world seems to know about what the OOI does or the secrets it keeps. Howard only begins to rise in the ranks and learn about the larger purpose of his day job when a defector—a person illegally (no visa, because they issue visas in the Prime world) hopping between the universes—comes into the regular world and starts assassinating folks seemingly at random. Howard Prime shows up to let the OOI know in confidence he believes there are moles among the worlds' bureaucracy enabling these killings, and he needs to work with the regular-world OOI higherups (plus Howard) to do something about this situation quietly.

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Ars has watched the first three episodes and will likely (and happily) blow through the next three very soon (Starz provided six in advance to press; the channel already ordered two 10-episode seasons). The violence can get intense, the scenery remains delightful, and the writing (led by relative newcomer Justin Marks, who is also linked to future Top Gun editions) stays clever. The show sprinkles in meditations on what makes us us (nature versus nurture) gracefully, and presumably that will only increase going forward.

Thus far, the spy story on its own merits a watch for any fans of the genre (in particular: when the first inevitable Parent Trap-switch takes place, the attention to detail of all parties involved plays out excellently), but the performances are what will keep Counterpart on critics’ watchlists. Olivia Williams (Rosemary from Rushmore) also does double duty, though with a lot more to do in one universe, and new-to-us actors like Harry Lloyd and Ulrich Thomsen (the first a reluctantly explain-y OOI official catching Howard up, the latter a steely counterintelligence agent) or Sara Serraiocco and Nicholas Pinnock (can’t say, #nospoilers) all prove likable quickly.

And Simmons’ performance may very well be the whole reason the show exists. The two Howards appear on screen together a fair amount, but you never for one second question which is which. Simmons somehow demonstrates both a shared DNA and a distinct persona in each of his characters. When some confused OOI individual asks who’s who, audiences are way ahead thanks to subtle cues like a slight slouch and pursed lip on Howard and the stiffening brow (followed by a quick f-you) from Howard Prime.

The distribution (Starz, aka where some devotees go for Outlander but should also checkout American Gods S1 at least) and familiar-ish premise may keep Counterpart from becoming some kind of cultural watercooler force, but Simmons' performance makes following the series worth it early on. So in a logistical sense, maybe Counterpart's best hope is to mimic the gameplan of another actor-centric showcase that debuted with little fanfare, earned its star some accolades, then had a decent long-term run thanks to the post-airing screening market. That show came along 10 years ago; I think it was called Breaking Bad.