With its first season in the books, WGN America’s period drama has proven to be a surprisingly addictive — and effective — series.

It doesn’t matter that you’re a good man. Maybe a good man couldn’t have made implosion work.

–Glen Babbit, to Frank Winter

Spoilers follow, naturally.

I reviewed Manhattan at the halfway point, and I’m pleased to remark that every episode in the season’s second half was superior to its first. Not only did the relationships and conflicts deepen, as the race to complete the first viable prototype of “The Gadget” continued, but I could see the series (created by Sam Shaw) becoming even more confident in construction and execution.

Take, for example, the season’s penultimate — and likely best– episode: “The Gun Model.” Several strong arcs converge at once. First, “Thin Man,” the code name for the group working the military’s preferred design, is on its last legs thanks to a discovery made by Charlie Isaacs (Ashley Zukerman, who became more compelling the worse things got): the plutonium will never be pure enough to keep the bomb from self-detonating — the design is doomed. This is why Isaacs has been secretly in cahoots with the prickly Frank Winter’s (John Benjamin Hickey, fantastic in a difficult role) “Implosion” team, violating the military’s sacrosanct compartmentalization policies, in order to have Thin Man’s scientists — unbeknownst even to them — doing calculations to make Implosion work.

The closing moments of Episode 8, “The Second Coming,” were a fist-pumper: Thin Man is screwed. Implosion, following a visit from one of the Allies’ top scientists, is also screwed — or so they think, until Isaacs shows up at Winter’s door: “So what are we going to do about it?” The two egos, who have been rattling each other’s cages since Episode 1, team up right under the noses of military brass — and Thin Man’s leader, Reed Akley (David Harbour, brilliant) to do what must be done to complete the project. Actually, not just complete it — but complete it faster than the Nazis. Winter can practically hear the footsteps of Werner Heisenberg when he goes to sleep at night.

But as we learn, heartbreakingly, in “The Gun Model,” Akley knew his design was flawed. That’s why he was so desperate to keep Charlie happy, naming him team leader while Akley went off to visit the plutonium plant in Washington state. But when he learns from Paul Crosley (Harry Lloyd, effortlessly charismatic) — himself spurned by Winter, but especially by Helen Prinz (Katja Herbers, ditto), who turned down his marriage proposal — that Charlie has been more or less “sabotaging” the project, the jig is up. Akley almost manages to keep Charlie back on his side, lecturing him about Frank’s ego, and how Frank is just using Charlie…and, the thing is — this is what the show does so well — Reed Akley isn’t entirely wrong. Frank is a jerk, having put his project’s success over human beings time and time again. In the season finale, “Peristroika,” Winter is haunted by Sid Liao, the Chinese-American man he gave up early in the season to keep federal investigators off his back.

Reed’s solution to his imminent failure, as the architect of the most expensive cluster-you-know-what in American history? To put a shotgun in his mouth. The fallout, of course, is massive. Occam, the malevolent “high inquisitor” played by Richard Schiff, is about to frog-march Isaacs out to face a firing squad for sharing government secrets — which, of course, he didn’t do, but they know Charlie did something shady. They know he framed Lancefield, one of Thin Man’s scientists, when he discovered Charlie was playing for both teams — much to the revulsion of Charlie’s wife, Abby (Rachel Brosnahan, so pale), who had actually fallen for Elodie, Lancefield’s wife.

Complex enough for you yet?

I haven’t even gotten to half of the cast,  with mini-arcs and secrets of their own. It’s a tangled web of motivations and ideals; wheels within wheels, where everyone has a clear point of view, and everyone fervently believes that they’ll not only be the ones to end this war, but — as Winter naively puts it — to end all war. The storytelling functions on multiple levels: it’s a period workplace drama, like Mad Men; it has its soapier elements, however benign; it’s a fictionalized account of one of the most important seasons in America’s history, but includes real, accurate science.

Most importantly, the driving thrust of the narrative — the industrial-military complex’s secret to end all secrets — is fully manifest in the personal and inner lives of its characters. How can these scientists function in the fabricated world of Los Alamos? Paranoia runs rampant, as it seems anyone can be accused, at any time, with sharing information. At the end of “Perestroika,” Winter beautifully turns this to his advantage, committing his first truly selfless act in the whole season, and right when he needed to the most. He had been told by another friend he betrayed, Glen Babbit (Daniel Stern), that he doesn’t need to be “a good man” to beat the Axis powers to the punch. And what’s one more casualty, to get Frank’s name in the history books as The Man Who Built the Bomb?

Except, Frank has one more trick up his sleeve. He fabricates an elaborate confession, knowing that Occam was listening, claiming that he and Akley were together from the start, and that it was Frank — not Charlie or anyone else — who leaked info to Germany. Suddenly, Charlie is thrust into that fateful meeting with Robert Oppenheimer and the Secretary of War, while Frank is driven away with a bag over his head. The season-closing montage, set to Papercuts’ “Future Primitive,” is a doozy, showing that anachronistic music can be just as effective if deployed well. (All of the show’s music is deployed well; the alt-electronica score from Jonsi & Alex is perfectly unsettling.)

Manhattan has a few flaws, though many were consciously re-calibrated as the season went along. (Here’s one: the show has no idea what to do with children, as the Winters’ daughter is bratty, and Charlie and Abby Isaacs seem to often forget their son exists.) What would have been eye roll-inducing on a lesser show — Abby’s out-of-nowhere fling with Elodie; Liza Winter’s (Olivia Williams) slow unraveling — ultimately resolved in fascinating places, even if the journey there was meandering. Even the thinnest character on Winter’s team, Jim Meeks (Christopher Denham) finally, finally had something to do in the final moments, as he was revealed to be the spy. Best of all, the show’s visual style evolved to the point where it wasn’t hammering the metaphors home, but landing in perfect balance with the writing. I loved the interrogation scene in the finale, the camera swooping from left to right, in and out, as Occam and Isaacs verbally sparred.

I can’t say enough good things about Manhattan, really. It was a slow burn, but right around “The Second Coming” it all started to coalesce, and I was completely hooked. The ratings, naturally, have been abysmal, but it’s heartening to hear that WGN America believes in the show enough to renew it for a second season. It’s my hope that a year from now, the buzz around it will have grown, and television connoisseurs everywhere will have binged on these first thirteen episodes, and line up for more. And if you’ve read this far in this review, I expect you’ll be one of them.

Season Grade: A-