'The Expanse' Season 4 Opens 'Second Movement' For Amazon Series

The end of The Expanse Season 3 opens thousands of alien worlds to humanity, with each new system accessible through a network of Ring Gates, built by an extinct society. The tense political situation between Mars, Earth and the spacebound Belters, who populate the solar system's working class, is now a galaxy-spanning powder keg.

"There's going to be a transition for sure," cast member Cas Anvar told U.K. newspaper Metro. "How much of it is Amazon and how much of it is just the fact that book four is a very different book, I don't know. We'll have to see. But the first three seasons, the first three books, are like the first movement of an opera. Book four represents the beginning of the second movement, and it's almost poignant that we've transitioned from one network to another broadcaster with Season 4, because it really is starting a new page of the journey for the Expanse family."

The Rocinante crew are going planetside in Season 4 of "The Expanse." Prime Video

On The Expanse, Anvar plays Alex Kamal, who pilots the Rocinante, a salvaged Martian gunship at the center of several interplanetary crises, many involving a mutating alien technology. Cast members gave more context on how The Expanse Season 4 charts a new course for the show while speaking to Collider at San Diego Comic Con.

"You also see all of the characters go through very different transitions and journeys that we've never seen before," Dominique Tipper, who plays Rocinante mechanic Naomi Nagata, said. "It's not the same thing as what we've had for the past three seasons. There's a bit of that in there, but it's also something quite fresh and exciting."

"It is a tonal shift," Steven Strait, who plays captain James Holden, said. "It has a frontier kind of vibe."

The Expanse Season 4 is based on Cibola Burn, the fourth book in The Expanse series, by Daniel Abraham and Ty Franck, who write under the joint pen name James S.A. Corey. Cibola Burn leaves the solar system for the alien world of Ilus, where independent settlers square off against establishment powers.

The cover for Book 4 in "The Expanse" series. Orbit Books

"The rings have opened up, there's an imminent gold rush, and what that does to the balance of power in the system, in the macro sense, is completely change the entire chessboard. And all this tension starts to build, in the macro and in the personal sense, everywhere, and it just changes everything," Strait added.

"And some us live," Wes Chatham, who plays Amos Burton, adds, to laughter from the rest of the cast.

The Expanse Season 4 premieres December 13 on Amazon Prime Video.