The new Apple TV+ series Silo, which premieres on May 5, is based on Hugh Howey’s SF book series of the same name, set in an underground city in a post-apocalyptic future. Thousands of people live in the silo, which is made up of 144 floors, extending deep into the earth; to go between levels, one must climb up and down seemingly endless flights of stairs. It’s been many generations since the fairly low-tech silo was built, and its origins are murky, as many historical records were long ago erased, allegedly by rebels. One thing everyone is certain about, though, is that the world outside the silo, up on the surface, is deadly. Very few people have gone out there, as volunteers or as convicted lawbreakers, and those still in the silo watched them die horribly on their viewscreens, poisoned by toxic air.

The book series modestly began as a novella, “Wool,” which Howey self-published in 2011. It was so popular that he continued the tale in four sequel novellas, which were traditionally published in print form as the collection Wool in 2012. In the original story, Sheriff Holston is the silo’s well-liked lawman, with a loyal deputy named Marnes; both serve under the benevolent Mayor Jahns. A few years earlier, Holston and his wife, computer tech Allison, finally got approval to have a child, but had no luck conceiving. Around the same time, Allison became preoccupied with the silo’s past, wondering whether the powers that be were telling the truth about what happened to the historical record—and soon she discovers something that makes her want to go outside. Years later, the sheriff also decides to go topside, where he makes a chilling discovery.

The next novella, “Proper Gauge,” follows other characters, including Marnes and Jahns, who convince Juliette Nichols, a tough-minded worker from the silo’s Mechanical section, to become the new sheriff—over the objections of the shifty, power-hungry head of IT, Bernard Holland, who wants to install his own man, Peter Billings, as the new top cop. Not long after Juliette takes the job, she finds herself looking into secrets of the silo, and asking very dangerous questions.

The first season of the show is based on these two novellas and stars David Oyelowo as Sheriff Holston, Tim Robbins as Bernard, and Dune’s Rebecca Ferguson as Juliette. (She and Howey are among the show’s executive producers, as is its creator, Graham Yost of Justified fame.) The first novella is dispensed with quickly—almost entirely in the first episode, a showcase for the reliable Oyelowo. After that, the show shifts to Juliette’s investigation into the death of her lover, George, which leads her into the mystery of the silo. This is a change from the original tale, in which George is barely mentioned, and she learns about the silo's secrets through other means. Still, this alteration gives Ferguson, a compelling screen presence, more to do as an actor, as Juliette deals with grief while slowly sussing out a whodunit.

Other changes are more significant. On the show, the silo’s Judicial section, under the control of a new character named Sims (Hell on Wheels’ Common), uses Gestapolike tactics to suppress curiosity and dissent—storming people’s homes, arresting people on trumped-up charges, and so on. It creates an atmosphere of constant terror that simply isn’t present in the novellas, which portray a much subtler version of authoritarianism.

The show also gives Peter Billings (Dickinson’s Chinaza Uche) a much-expanded role. In the novellas, he’s just a tool of the crooked Bernard; in the series, he’s a by-the-book deputy, secretly suffering from an ailment like Parkinson’s, who begins to have doubts about the rightness of his cause. He’s an intriguing character, and Uche gives a fine, nuanced performance. Ultimately, though, Billings has little effect on the plot. Indeed, the story ends up in the same place as the brisk, efficient novellas do, despite all the extra material.

The series isn’t helped by the fact that the silo simply isn’t very interesting to look at—mostly brutalist concrete structures with occasional steampunk-ish touches to break up the monotony. One exception is the silo’s power generator: a massive, whirling contraption that provides the focus for one of the most suspenseful episodes. In the end, though, there’s only so much gray and brown that a viewer can take. Fortunately, the mind’s eye can supply more interesting visuals, and there’s plenty more to read in the Silo series, including three more Wool novellas; a series of prequel novellas, collected as Shift; and a sequel novel, Dust. The show will likely get to them all at some point—but if this season is any indication, it may take a while.

David Rapp is the senior Indie editor.