“9-1-1: Lone Star” boss teases season 5: Grace's exit, arrival of TK's half-brother, and an epic train derailment

Co-showrunner Rashad Raisani shares what's in store after actress Sierra McClain's unexpected departure and the death of Carlos' father.

The key to an easier start of a 9-1-1: Lone Star season? An ambitious season finale.

"It was a bit self-serving, but we intentionally left season 4 making sure that we had big stories to explore in season 5, so we didn't have to get back into the writers' room and go, 'Gee, what are we going to do this year?'" co-showrunner and executive producer Rashad Raisani tells Entertainment Weekly of planning out what has now been announced as the final season of the Fox first responder drama. "We wrote a check on several fronts."

Those "fronts" include TK (Ronen Rubinstein) and Carlos (Rafael Silva) getting married just days after the murder of Carlos' father, Gabriel (Benito Martinez); Owen (Rob Lowe) assisting in the euthanasia of his half-brother Robert (Chad Lowe); Tommy (Gina Torres) getting more serious with Pastor Trevor (D.B. Woodside); and Judd (Jim Parrack) leaving the 126 firehouse to care for his son, Wyatt (Jackson Pace), who was hit by a car and left partially paralyzed.

Related: Rob Lowe thinks 9-1-1: Lone Star will conclude with season 5: 'It is the end of an era'

Those were the twists they planned, but then there's what Raisani refers to as "some off-screen stuff that also shook up our world," meaning the departure of actress Sierra McClain, who starred as the main 911 call center dispatcher — and Judd's wife — Grace for the first four seasons of the show.

"The first thing I would say is we all adore Sierra McClain. If not for her, we wouldn't be talking right now. She's a central piece to the show. She's the voice on the phone of the title, you know what I mean?" says Raisani. "And we didn't know [she was leaving], so we had stories [for her]. Then when this stuff happened, we had to go back to the drawing board in some storylines. You have no choice but to find silver linings, let me put it that way. If Sierra was willing to come back.... As I told her, 'Any time I'm here, there'll always be a place for you.' I would love it, I'd beg her. But [her departure] did force us to do some unexpected things that led to some beautiful storylines."

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One of those storylines centers on Pace's Wyatt, who was intended to guest star on a "few episodes" this season but was upgraded to a series regular and will serve as the show's new dispatcher — a pivot from a previously planned arc: "We thought maybe he'd start to work in the call center, and Grace would be his mentor, and that would be a nice story to play," says Raisani. "We wanted to show that no matter what your physical situation is, you have so much to offer. I'm proud that we're able to tell that story for a lot of people who may have something that makes them feel like they have struggles, but to see that there's always ways that you can do something great. So [McClain's departure,] I think, ended up being a fortuitous thing in allowing us to go bigger with that storyline."

But where does that leave Judd? "He is kind of finding himself a bit adrift," says Raisani. "His purpose is in his job, his purpose is with his wife, his purpose is with his son — and all those things leave him almost at once, and that's where we kind of meet him. So that's going to have ramifications for the whole season, really. He's a man whose life has been shaken to the core because of things that have happened, both for good and for bad."

Then there's the "big game-changing stuff, massive things for these characters that are going to shake up their worlds" that Raisani and his team actually had planned for the Lone Star crew, including Carlos following in his late father's footsteps as a Texas Ranger, the arrival of TK's half-brother, and Owen's emotional turmoil over his role in his Robert's death.

"Marriage is not the end, in many ways, it's the beginning," Raisani says of newlyweds Carlos and TK's journey this season. "We said in season 3 that TK had a younger sibling, Jonah, [who is the son of TK's mom and stepfather, Enzo,] who raised TK, really. And along with TK's backstory coming in, Carlos has this giant mystery of his life: Who killed his dad? And that's not just going to be a procedural story, it's an emotional one as well that's going to affect TK and Carlos's relationship.

"And for Owen," Raisani continues, "I felt like we couldn't just walk away from what we did at the end of the season, which is that his brother died in a way that only Owen knows the truth of. There's more to that story than we revealed on camera, and it's going to haunt Owen, as you'll see very gently in these first episodes. But it comes to a head later, and we'll find out that there's actually much bigger twists in what happened, and that will come out."

Back at the firehouse, Marjan (Natacha Karam) and Paul (Brian Michael Smith) will be battling it out to see who replaces Judd as lieutenant of the 126. "Part of what we wanted to play here is that they are best friends, but they're kind of lying to themselves when they say this won't affect their friendship," Raisani says of the characters' new dynamic. "For their friendship to mature, they have to go through this crucible and also acknowledge that, 'You know what? I can be best friends with you and still really want this bad.' But we're going to push it to the limits in episode 3 and we really see who they are and what their friendships mean to each other and this competition."

Part of what will test their friendship and leadership skills under pressure is the derailment of a train carrying cargo that could put all of Austin at risk — a storyline Raisani says they had originally discussed for season 4. "Thematically it just didn't fit with the stories we were telling last season," he explains. "But it works much better into the story this year. And the team had already done all the [research and development] on how to maximize the emergency [on screen] without creating a natural disaster ourselves or creating a natural disaster for [production company ABC Television's parent company] Disney's budget!"

The apparently very well-planned 9-1-1: Lone Star season 5 premieres Monday, Sept. 23, at 8 p.m. ET, on Fox.

Read the original article on Entertainment Weekly.