Balfe plays Rose, described in the official logline as "a relentless documentary filmmaker and recently divorced mother, brilliant at uncovering others' truths but struggling to resolve her own." When Rose begins investigating a 20th-century cult called the Church of Ascension, she finds "unexpected refuge" in its teachings before uncovering something "far more insidious" underneath, according to Variety.

The series draws its inspiration from Adam Nevill's novel Last Days, a connection confirmed by both Apple's release and The Hollywood Reporter. Neither source specifies how closely the show follows the book's plot.

Coverage of the announcement hasn't settled on a single genre label. Apple's press release calls Ascension a drama. UPI describes it as a psychological horror thriller, and Variety calls it a horror thriller outright. Apple's release doesn't reconcile the three descriptions, so for now they sit side by side.

Casey Affleck was the actor attached when Ascension first made headlines in 2017, per Variety's report. Balfe is attached to the version Apple has now ordered, though the available reporting doesn't say whether the script or the character changed between the two attachments.

The show's writing credits are split four ways: Natalie Erika James, Christian White, Alfonso Cuarón and Carlos Cuarón, according to Apple's release. James and White will co-showrun the series, with James also serving as lead director. Cuarón's credited role is writer and executive producer, under his overall deal with Apple. James and White have worked together before, on the horror films Relic and Apartment 7A, according to The Hollywood Reporter.

That arrangement looks different from Cuarón's last Apple TV project. Disclaimer, a seven-part series written and directed by Cuarón, starred Cate Blanchett as a documentarian confronting a secret from her past, according to NPR. The show was based on Renee Knight's 2015 novel The Perfect Stranger and also featured Kevin Kline, Sacha Baron Cohen and Lesley Manville. NPR described Disclaimer's story as one that evolves steadily across its seven episodes, though the review noted some viewers may find the ending overly manipulative and a little too pat.

Disclaimer's single-author structure doesn't carry over to Ascension. Writing and directing responsibilities are split among four credited writers and two co-showrunners, with James also directing.

Ascension comes from Apple Studios, with Anonymous Content producing, the same combination behind Disclaimer, according to The Hollywood Reporter. Cuarón's overall deal runs through his production company, Esperanto Filmoj, per the same report. Anonymous Content also produces two other forthcoming Apple TV series, Neuromancer and 12 12 12.

For Balfe, Ascension is a second project with Apple. She's also set to appear in Apple Original Films' Tenzing, according to Apple TV Press.

Apple's release names Balfe as star and lists the writing and directing credits, but it stops short of a premiere date, an episode count, or any cast beyond Balfe herself.

A premiere window and the rest of the cast remain unannounced. Apple has confirmed the series order and the creative team behind it; everything else awaits a further release.