The continued success of The CW's iZombie ultimately comes down to one thing: its ability to evolve. Each season the show ups the dramatic stakes by taking bold risks that somehow change everything and nothing at the same time, and it's a testament to the quality of the writing that it can take these kinds of narrative leaps and not only come out the other side better than it was before, but with its sense of humor firmly intact.

The most obvious example of this was the show's decision to reveal the existence of zombies to the masses after a large sector of the Seattle population was infected with the zombie virus at the end of Season 3. What could have spelled doom for the little zombie show that could — where would the show go if everyone knew about zombies? — has ultimately allowed the series to grow and still maintain everything about it that made it great.

At the start of Season 4, Liv (Rose McIver) is still working with Clive (Malcolm Goodwin) to solve murders, only now she's doing it in the open and with everyone knowing the truth about how she helps Clive catch the culprits. This allows the show to maintain its case-of-the-week format in the wake of a major change, and it in turn provides a sturdy foundation that can support the inevitable expansion of the show's overarching narrative.

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But with this new development also comes a number of changes in the way the walled city of New Seattle and the show itself operate. Not only are the memories zombies see while on brains inadmissible as evidence, but there are city-wide curfews enforced martial-law style by Fillmore-Graves mercenaries like Major (Robert Buckley), who is once again a zombie, likely for good. There's also a no-tolerance policy for zombies when it comes to scratching humans (the premiere revealed Chekhov's guillotine early on); anti-zombie gangs known as Dead Enders who threaten the city's zombie population; and an entirely new set of laws that are meant to govern the undead and how they are integrated into society.

Robert Buckley, Rose McIver and Malcolm Goodwin, <em>iZombie</em>Robert Buckley, Rose McIver and Malcolm Goodwin, iZombie


Because of these significant changes as a result of world-building, iZombie's fourth season is more overtly political than previous seasons, drawing obvious parallels to war-torn cities whose inhabitants are engaged in a never-ending battle for control. There's currently a shaky truce between the zombie and human populations, as the latter's existence is what keeps Seattle from being bombed off the map entirely by the U.S. government, but Fillmore-Graves and its employees are working overtime to make sure it holds. The good news is, even as the show tackles stories about black market brain operations, coyotes ferrying people in and out of the city, and zombie teenagers being thrown out of their homes because they've been disowned by their parents, the show's heart and sense of humor remain unchanged.

In the season premiere, Liv eats the brain of a man who hates zombies but loves the Seahawks. Although the mystery itself isn't the show's most engrossing to date — a mother murders the father of her son after he kicks the teen out for being a zombie — it doesn't matter, because the case plays into the overarching themes of Season 4 while still allowing the show to have a bit of fun with Liv, who frequently ignores or forgets she is the very thing she's supposed to hate.

Meanwhile, Liv's obsession with the Seahawks is the source of a few good jokes about the 49ers, but it also strengthens the identity of the city at the heart of the show by highlighting the way this new zombie world order affects every aspect of life in and around Seattle. This theme continues throughout the episode as Blaine (David Anders) is now running a new restaurant where humans and zombies can eat side by side, an operation he describes as "cemetery to table," and the Scratching Post is booming now that zombies are living out in the open. Nearly every aspect of the show is clicking in the wake of its largest risk to date, and not even the reveal that Ravi (Rahul Kohli) is a human with zombie tendencies once a month as a result of the zombie vaccine is enough to drag down the good mood created by the knowledge that after three seasons, iZombie is still one of TV's most consistently entertaining series.

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David Anders, <em>iZombie</em>David Anders, iZombie


But if there's one aspect of the show that does give pause in the wake of zombies becoming public knowledge, it's the introduction of a storyline involving religious fanaticism via Blaine's undead father Angus (recently promoted series regular Robert Knepper), who's been released from his personal prison inside a well. It remains to be seen how this particular corner of the show's universe will play out within the larger picture — he's only in the beginning stages of gathering an army of undead followers by the end of the premiere — but until we see where the show intends to go, it's hard to tell if this is a rare misstep for iZombie or just the latest development in a show that thrives on challenges.

Still, you don't have to eat a brilliant scientist's brain to know that not every bold move the show makes will net it positive gains. But iZombie has found success by taking daring leaps of faith before, and even if this storyline doesn't ultimately come together in the long run, a few mistakes likely won't hurt a show that's as reliable as iZombie has proven itself to be.

iZombie airs Mondays at 9/8c on The CW.

(Full disclosure: TV Guide is owned by CBS, one of The CW's parent companies.)