Silo is such a complicated show that even its showrunner gets confused sometimes. While filming the final seasons of the Apple TV sci-fi thriller, Graham Yost remembers two instances where he messed up details: once it was an actor who realized that a conversation they were about to shoot should’ve already taken place, the other involved the Japanese localization team pointing out that a subtitle didn’t match what was going on onscreen. In both instances, the problem was ultimately fixed, but Yost’s reaction was the same: “Oh shit, you’re right.”

Keeping everything straight is one of the big challenges of working on such a complex series, and as Silo enters into its final two seasons, the challenge has only increased. So it’s a good thing Yost has a team working alongside him looking for those mistakes. “It’s a lot to keep track of, but everyone is pitching in,” he says, “and I love this sense of collaboration.”

Season 3 of Silo starts streaming on July 3rd, and it expands the story’s scope quite a bit. The series follows the lives of the residents of a huge underground bunker hundreds of years in the future. The silo is home to 10,000 people who essentially live in a vertical city, one divided into layers that each have their own jobs and cultures, from the mines at the bottom to the government up top. The only way to navigate the silo is through a massive spiral staircase that goes from top to bottom, creating a very physical form of class division.

Initially it seemed the residents were the last remnants of humanity living in a postapocalyptic wasteland. But over the course of the first two seasons, it became clear that they lived in but one silo of many, each housing their own communities while isolated from the rest. Season 3 adds a new wrinkle: showing how the world came to be this way in the first place, a process that starts in a world that looks much like our own.

The season 3 premiere constantly jumps back and forth between the bleak future where we’ve spent the last two seasons and our present day, when the decisions were made that led to everyone being trapped inside of underground bunkers. Things are already complicated as the show picks up from last season — protagonist / silo mayor / reluctant revolutionary Juliette (Rebecca Ferguson) has just become the first person to venture between silos and is now suffering from memory loss — and the multiple timelines only ratchets that up.

The cast of Silo all have different techniques for dealing with this challenge, which becomes even harder given that scenes are rarely shot in chronological order. For some, daily team meetings with directors can be an invaluable tool. “A lot of days, we’d start the day with story time, and the director would go through where we’re at, where we just came from, what happens next,” explains Alexandria Riley, who plays newly promoted authority figure Camille Sims in the show. “It’s already a complicated story anyway, but then when shooting out of order, you do get a bit foggy.” Ferguson notes that the hair-and-makeup team can be particularly helpful in tracking the story, as they need to be on top of things like scars and burns to maintain consistency. Every detail counts. “The little changes that you do have enormous ripple effects going forward,” she says.

“It’s a lot of pieces you’re trying to put together,” adds Common, who plays Camille’s husband Robert on the show. “It is our job to know where we are, but thank god we had support, too. There are times when I’d have to talk to Alex about something just to be reminded.” The two actors even had separate rehearsals together to make sure they had everything down.

Others took a different approach. Jessica Henwick, for instance, joined the main cast as the present-day investigative reporter Helen in season 3, and says that “I didn’t read any scenes except my own. Because I’m a fan of the show, I wanted to preserve that experience. I will watch season 3 as a fan and see what happens. I don’t know what happens except in our storyline.” (Henwick is such a fan that, soon after she was cast, she had a single goal in mind: “I went to the set and explored the stairs.”)

One thing that doesn’t help much, however, is delving into the source material. Silo is based on a trilogy of books by author Hugh Howey; the first two seasons explored the first book, while the final two will wrap up the rest of the story. But much has changed in the adaptation as the TV show attempts to both make Juliette a more visible figure in the central part of the story and update some of the plotlines to reflect present day concerns like AI.

“I started reading the books and realized very quickly that that wasn’t going to help, because the books are so different,” explains Ashley Zukerman, who plays a congressman in the present day storyline. He says that keeping both the novels and the TV show in his mind at the same time wouldn’t be helpful and instead found “that reading the whole scripts and then finding a way to forget [what his character wouldn’t know] was useful.”

With two seasons to go, Silo is racing toward a conclusion as it attempts to wrap everything up. Yost says that four seasons was always the plan, so the process has been figuring out how to fit everything into a set number of episodes. But since the final two seasons were filmed back to back, it also means that the Silo team are done having to worry about keeping all of those complicated plotlines straight. And as much as she says she’ll miss the experience of working on the show, there is one thing Ferguson is excited to be done with beyond memorizing storylines.

“I fucking hated running up and down those stairs,” she says.