Although it was among the best shows on TV last year (the best, according to yours truly), HBO’s dark comedy “Barry” also made a strong, if unintended, case for the one-and-done theory of superior television: If a single season is so taut and fully realized that its finale ends on such a memorably symmetrical (and conclusive) note of dread, why not call it a day? Why not admire its sublime perfection and agree to walk away?

The answer, of course, rests in one of the great promises of the medium: In TV, more isn’t merely a suggestion; more is the ideal state of being. “Barry,” created by Alec Berg and Bill Hader, returns Sunday with almost no trace of encore jitters or apparent concern of painting itself into potential plot corners.

Instead “Barry” takes us deeper into the wounded heart of darkness belonging to its title character — played by Hader, who won an Emmy for his performance in Season 1, along with nominations for writing and directing. The show now further explores Barry’s ability to compartmentalize his life as a ruthless hit man for hire who is responsible for killing so many people (including the L.A. detective who tracked him down) with the part of himself who aspires to be an actor, finding unexpected happiness in workshop classes taught by Gene Cousineau (Henry Winkler, “Barry’s” other big Emmy winner).

Picking up a few weeks from where Season 1 left off, “Barry” steps back to expand on its flawed protagonist’s delusional hope that his criminal days are behind him, even as Detective Loach (John Pirruccello), the bereaved partner of the missing/presumed murdered Detective Moss (Paula Newsome), picks up on the leads she left behind, which brings Barry’s estranged boss, Fuches (Stephen Root) back into the picture.

To that, add the reappearance of fan-favorite NoHo Hank (Anthony Carrigan), the hilariously inept Chechen mob boss who ascended to power after Barry murdered Hank’s boss. Hank now needs Barry to help him eliminate a newly arrived Burmese crime lord who wants a piece of Hank’s cushy partnership with a Bolivian drug cartel.

The idea, obviously, is that Barry can only continue to sink into the moral quagmire that requires his sharpshooting prowess, no matter how much sympathy we feel for him. It’s a throughline handled as expertly as those flawed-men dramas that held us in such anxious sway a decade ago (Don Draper, Walter White, et al). Who would have ever thought Hader would so confidently, so compellingly fill those shoes? It’s a thrill to watch him channel his deadpan side into this quietly conflicted killer.

“Am I evil?” Barry asks NoHo Hank, hoping to be reassured of his own humanity.

Oh, my god,” Hank replies in his Chechen-meets-Insta-Influencer accent. “I mean, absolutely. Do I not tell you that enough? You are, like, the most evil guy I know.”

The season’s first three episodes, made available for this review, frequently flash back to Barry’s tours as a Marine in Afghanistan, where his skills as a sniper brought him the sort of acclaim that he now seeks from acting.

Cousineau, still mourning the loss of Detective Moss (who had become his girlfriend), urges Barry to repurpose his war trauma on the stage. Barry’s ambitious but oblivious girlfriend, Sally (Sarah Goldberg), also unwittingly prods him to explore his damaged side. Neither is aware this man is a powder keg.

“You have got to get in touch with your inherent darkness,” Cousineau nags.

“It’s not inherent — ” Barry starts to reply.

“Trust me, that’s exactly what it is, and it is dark. And you better funnel it into your work or there is the damn door.”

The darkness gets darker, yet “Barry” is sticking to its comedic intent and half-hour format. This is remarkable, given that it plays as intensely and satisfyingly as “Breaking Bad” once did. Here, however, the one who knocks would give anything to not have to be the one who knocks.

Barry (30 minutes) returns Sunday at 10 p.m. on HBO.