After the mid-season sackings of two showrunners, production being temporarily suspended due to lack of filmable material, sweeping budget cuts and endless squabbling between Robert Kirkman, creator of the graphic novel, and the network and writers, it would be fair to say that The Walking Dead can seem a turbulent show.

And yet, so far, a sedentary second season has been the only visible signifier of trouble behind the scenes. Ratings remain strong, as does the cast, and the last season (which introduced us to David Morrissey’s despicable baddie, the Governor) was, arguably, the best yet. Still, with yet another showrunner now in place – who may be wondering whether it’s even worth taking his coat off – I worried that the show’s latest snafu might be one snafu too many, and approached the fourth series with trepidation. Five episodes into series four, and I’m delighted to discover that it’s all going rather well.

Following the battle with the Governor last season, the prison was safe. Too safe, in fact: zombies, for all their incorrigible brilliance, are perplexed by moderately high fences, and as much as we love these characters, watching them effectively farm pigs or perform perimeter sweeps is about as much fun as going outside and performing these tasks ourselves.

To address this, season four has focused on a deadly pathogen sweeping across the camp. An outbreak of the sniffles isn’t as foreboding a notion as a scene-gnawing Morrissey or a vast horde of the respirationally challenged, but the disease (and the previous revelation that, however someone dies, they will become a walker) has allowed the writers to wring gallons of tension and emotion – and, yes, blood – from it. Zombie outbreaks within the prison’s walls shook its residents from somnambulance: the first battle in the cellblocks was a furiously exciting statement of intent for the series; the second, in episode five, better still. Most new additions to the group have been drafted in solely to have their faces gnawed off, but their deaths, which have been legion, sold the disease as a formidable threat. Crucially, they also allowed Herschel to further solidify his stature as the Best Person Ever by exposing himself to infection to attend to the ill before metamorphosing into a shotgun-wielding badass, like some beautiful hybrid of James Herriot, Bruce Campbell and Richard Attenborough.

This series has also seen irksome character traits of the third season wisely eschewed: Rick’s hallucinations were becoming tiresome and trite, and rent-an-idiot Carl was fast becoming someone you would never tire of punching in the larynx. Both of these niggles have been excised, with the renewed relationship between the two becoming a genuine highlight. Carol, too, has displayed a brutal, refreshing new pragmatism following duff storylines in the first two seasons; it was heart-wrenching to see her banished from the group she had been a part of since the beginning. Her exit did leave her as a tantalising, Merle-esque dangling thread – one I hope is yanked very soon.

Andrew Lincoln as Rick Grimes: one of four original cast members remaining. Photograph: Frank Ockenfels 3/AMC

This does leave Rick, Carl, Glenn and Daryl as the only original cast members, following the deaths of Merle, T-Dogg, Andrea and Lori last season, in a cull of surprising scope, even for this slash-happy show. In giving inevitable screentime to new additions, however, perhaps Daryl (second in line to the award of the Best Person Ever) is the character most in danger of being marginalised, though he has yet to deal fully with Carol’s departure, and sexual tension between the two has been palpable. Is he going to turn his attentions to Michonne without even a thought for poor Carol? I doubt it.

Some of his screentime is being surrendered to Michonne, the best addition to the cast since the show began. The return of the Governor will hopefully see her newfound benevolence come to an end in a crescendo of whirling katanas and lopped-off limbs, and the promise of her inevitable showdown with Morrissey is a hugely positive omen for the rest of the series. Other relative newbies are faring less well: Tyreese is little more than a clammy ball of coiled grumpiness; accident-prone alcoholic Bob Stookey can’t meet the molars of the undead soon enough; and the show has seen fit to replace annoying kid Carl with two more annoying kids.

The biggest worry is that this season will fall into the trap that befell season two, dulled by a single setting and narrative bagginess. A prison is a more interesting location than a farm – because, well, so is anywhere – but the last season was split between the prison and Woodbury, benefiting hugely from a broader scope. We’re five episodes into this season, and it’s difficult to argue that a huge amount has actually happened beyond a trimming of numbers, Carol leaving and some dead rats being left by a fence. But it’s never once been boring.

With the triple of threat – walker, disease, Governor – now established, the series feels as if it is truly hitting its stride. Encouragingly, as the next season has already been commissioned, the show as a whole appears to be in rude health too. Considering the extent of its backstage wrangling, this is both a relief and a minor miracle.