9 Things to Know About The Expanse Season 4, Straight From the Cast

In the year and a half since The Expanseaired its last episode, it was canceled by Syfy, saved by Amazon, and somehow seemed to only grow in popularity. Now, The Expanse is set to make its triumphant return to our screens with its anticipated fourth season, which is dropping all at once on Friday, Dec. 13.

Season 4 will find the crew of the Rocinante -- Holden (Steven Strait), Naomi (Dominique Tipper), Alex (Cas Anvar), and Amos (Wes Chatham) traveling through the Ring Gate to a new planet, Ilus, on orders from Avasarala (Shohreh Aghdashloo) to look for evidence of the protomolecule. But their mission runs into a few unexpected (and potentially fatal) challenges, including the tension between the belter refugees on Ilus and the U.N. envoy from Royal Charter Energy, who were given a charter by Earth for scientific exploration of the planet, which they've dubbed "New Terra."

The 10-episode season will largely follow the events of the fourth Expanse book, Cibola Burn, but fans of the novels can expect a few surprises along the way as well. "The thing that we've done is we're rubber banding the story," Ty Franck, who co-wrote The Expanse books with Daniel Abraham and acts as an executive producer on the show, told reporters on a recent press trip to Toronto. "So we'll diverge a little bit in the middle of a season and then we'll come back to where the book is."

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TV Guide recently visited the set of The Expanse, which is currently filming Season 5, to speak with the cast and creatives behind the sci-fi drama about what's next for the crew of the Roci, what they'll find on Ilus, and more. Check out nine things we learned about Season 4 below!

1. Ilus will present previously unimagined dangers.

The Roci crew has already survived unheard-of threats, but when they arrive on Ilus even they won't be prepared for what they encounter. Every aspect of the planet seems designed to harm, if not kill, the humans who have settled on the strange new land. And since no one has encountered anything like what they're facing before, they're left completely unprepared as to how to protect themselves.

The season plays on the idea that "when you go to a new place, anything there that isn't trying to kill you doesn't know you exist. The minute something realizes you exist, it's going to try to kill you because that's how nature works," said Franck. "It goes both ways," he added. "Obviously the Spaniards showed up in South America and everything tried to kill them. And then the invisible things that lived in their bodies killed everything. The minute two biologies start to mix, it's deadly for both."

While Season 4 will include most of the terrifying obstacles and new creatures on Ilus that were outlined in the books, there is one aspect of the planet's unique ecosystem that didn't make the cut. "I didn't get my mimic lizard, which made me very sad," Franck said. "He was a little lizard in the books that we didn't get to have because he would have cost one jillion dollars and the studio didn't want to pay one jillion dollars. So we didn't get him. But we got all the other stuff."

2. We're getting a ruthless new antagonist.

As if the planet essentially trying to kill everyone on it wasn't enough to deal with, the Roci crew will also come up against the merciless leader of the RCE team, Murtry (Burn Gorman). Having lost several of his people during the RCE shuttle's landing on Ilus, as a result of either an accidental crash or a terrorist attack, Murtry's preexisting dislike of belters boils over once he reaches the ground. And with any semblance of an established legal authority still months away, Murtry is quick to take advantage of the situation and does whatever he can to position himself as the true power on "New Terra" -- and evict the belters so he can profit off Ilus' plentiful lithium deposits.

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His lack of an ethical framework and willingness to kill to get what he wants will immediately put Murtry at odds with Holden and Amos. "When [Amos] sees Murtry, when he gets to know who he is, and what his objective is -- and he knows Holden and what Holden's objective is -- [Amos] knows that they can't exist in the same place together," Wes Chatham said, adding that Murtry also quickly recognizes the inevitability of the trio's collision course. "We know it's not going to end well. We know it. We're just waiting for the rest of the people to figure it out."

3. The Belters will find their entire existence threatened.

Despite holding on to one of the most valuable pieces of political leverage in the new world, Medina Station, the future of the Belt will be in jeopardy in the wake of the Rings opening. With hundreds of potential new planets with free air and resources now available, many belters want to abandon their home to go through the Rings and try to live down a gravity well. And even those who want to stay in the Belt are rightfully worried they will only become further disenfranchised, if not completely forgotten, and die out, while humanity turns the march of progress toward these new worlds.

As a result, the OPA will become more fractured than ever. This will put Drummer (Cara Gee), who remains in charge of Medina Station, in a particularly tough position where her leadership will be challenged like never before. "Because she has fought for Belter sovereignty in this particular way, with every fiber of her being, she has trained, she has pushed through such intense physical pain, emotional pain, spiritual pain, all with this sort of very particular image of what a unified Belt looks like. And so now that that has shifted so radically, it definitely shakes her sense of self and her approach," said Cara Gee. And when someone from Naomi's past resurfaces this season with bold new ideas for the Belt's future, the rift between the various factions will only grow and Drummer will find her loyalties tested in more than one way.

4. There will be a few surprising romances.

This season will see both Amos and Bobbie (Frankie Adams) enter into ongoing sexual relationships, neither of which is without its complications. Amos will strike up a fling with Murtry's right-hand officer, Wei (Jess Salgueiro), whose similarities to Amos draw the pair together but also might prove to be a ticking time bomb in the end. "I think that Amos has always used sex -- amongst all these other things, alcohol and violence -- as a way to kind of escape or run from the things that he's ultimately dealing with," Chatham said. "I think initially the relationship that's built with [Wei], that is what the intentions are. But it starts to get more and more intimate than he expected."

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Meanwhile, Bobbie will begin a casual relationship of her own with a fellow Martian veteran, which was a storyline that challenged Frankie Adams to discover new aspects of her character. "Honestly, I wasn't sure what her sexuality was. ... But it was really exciting to explore that human side of her that nobody's seen or thought of before," Adams said.

5. This will be a tough season for Naomi.

Naomi will go outside her comfort zone this season, both physically and emotionally, more than we've ever seen her do before. In addition to revealing more about her painful past, Naomi will also go down the well for the first time when the Roci lands at Ilus, an experience that will push her body to its limit. And even as Naomi struggles with unforeseen obstacles, she will do whatever she can to fight through her struggles and stay with her crew.

"I think it's pride, I think it's her Belter identity. I think it's the fact that she feels a responsibility as the only Belter in the Roci crew to be on the ground. I think she wants to be there," Dominique Tipper said of why Naomi chooses to go through the taxing process of going to the ground. "I think it's also about her relationship with Holden and giving them an option that is an atmosphere that isn't Earth, 'cause she would never be caught dead on Earth. So for her there is [the idea] like, 'Let's see ... if this is an option for us. If you did want to see a sky, we could come here.' So I think there's a lot of things riding on this for her, and to not try or not carry on is not an option for her."

6. Bobbie will go to some dark places in her search for purpose.

Although Bobbie never hesitated to give everything she had for Mars, when she returns home she's given nothing in return except a dishonorable discharge and a crappy job on the docks -- although she's lucky to have a job at all. The once prosperous and powerful planet is now crumbling, and Bobbie struggles this season to accept what's happening with her homeland while also being forced to discover her identity outside of being a Martian marine.

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During Bobbie's quest for her identity, she'll find herself falling in with a group of people who seemingly represent everything she had previously stood against in a storyline inspired by the novella Gods of Risk. While Bobbie's integrity will be challenged, these circumstances will help her find a stronger sense of self outside her suit. "She's really out of sorts, I think, at the beginning. And then strangely that becomes quite exciting for her," Adams said. "She has something to do. She has people to see, money to make, and she's doing what she was doing, but on her own terms."

7. Avasarala will run for office.

In an exciting original storyline for the series, Avasarala will have to run for office for the first time opposite her former employee Nancy Gao (Lily Gao), who has very different ideas of how to address the worlds on the other side of the Rings. So in between trying to save the world and prevent another Eros catastrophe, Avasarala will also have to campaign and -- worse yet -- consider public opinion.

"The whole election of Chrisjen Avasarala was a thing that we had always talked about for the books but had never done it," Franck said. "Because obviously she is a politician who's never been elected, and what is that like when somebody who has never been elected has to run for office for the first time? ... She's not a person who tolerates being questioned, and having her run for election where all people do is question every decision she makes and put a lot of demands on her time, that was a lot of fun," he teased.

8. We'll learn more about what makes Amos tick.

One of the most charming things about Amos is that even while the universe around him changes, he always seems immune to its effects. "He's the rock on which everything else breaks itself," Franck described. That remains true in Season 4, but for the first time viewers will start to understand how Amos became the person we see today once he is forced to stop relying on the crutches he created to keep the world at bay.

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"Amos' physical strength, Amos' intelligence, Amos' ability to be violent and quickly violent are all things that protect him, and it gives him control of the environment," explained Chatham. But when Amos finds himself in a circumstance that strips away all those control mechanisms, viewers will get to see "the fear that is underneath all those mechanisms" for the first time.

9. Holden will find himself questioning Proto-Miller's agenda.

The last time Holden put his trust in Proto-Miller (Thomas Jane), he saved the day. But this season will find the dynamic between Holden and Proto-Miller challenged once they arrive on Ilus, where Proto-Miller hopes to discover answers about what killed its creator. Holden is aware that he's walking on a knife's edge with his relationship with The Investigator, but that won't stop him from continuing to trust him at the beginning of the season -- which might not prove to be the smartest decision in hindsight.

"The prospect of him being used by the protomolecule is a very real and apparent danger, not just to him, but to everyone else on Ilus and possibly everyone beyond the Rings as well," Steven Strait warned. "It is a deeply complex and nebulous set of meanings for Holden to understand what Proto-Miller is to him, whether he knows what it is, whether it even matters whether he knows what it is. But certainly when it starts creating situations where everyone he's responsible for is in peril, he pushes him away in a lot of ways. But ... The Investigator evolves too."

As to what Strait means by that, showrunner Naren Shankar did offer one small tease that will be like catnip to book fans: "Miller Bot."

The Expanse Season 4 will be available to stream Friday, Dec. 13 on Amazon.