The penultimate episode of The Expanse’s fourth season just keeps the tension ratcheted and everybody holding for dear life. Saeculum was written by Daniel Abraham and Ty Franck, known collectively as James S.A. Corey, the authors of The Expanse series. Like the rest of the season, this episode dropped on 13 December, 2019.

Time is running out everywhere. Problems arise in orbit for Alex (Cas Anvar) and Naomi (Dominique Tipper) aboard the Roci as Murtry (Burn Gorman) authorizes a launch against them, while on Ilus, Holden (Steven Strait) connects with a struggling Miller (Thomas Jane) who is fighting his protomolecule controls to guide Holden to something at may stop the problems on the planet, and issues with the protomolecule itself.

As Miller guides Holden deeper into the alien structure in search of this potential ‘bomb’ to stop the protomolecule, Murtry sets off after them. And despite being given a warning by Amos (Wes Chatham), Chandra (Jess Salguiero) goes with Murtry.

And you just know that is going to end badly for all parties involved.

And it certainly does as Amos makes a decision, and then is wounded by an attack from Murtry before the rat scampers after Holden, who temporarily stops him, but he may not be able to stop the protomolecule from taking over Miller again and triggering something on the planet.

Or is it the right Miller?

We are left wondering as the episode closes out with Holden yelling to stop before the Miller-thing can cross over the barrier and bring everything to…?

Cibola Burn closes out the season and sets up the fifth. In fact, we learn pretty quick that what happened at the end of the previous episode rendered the protomolecule on Illus inert, the settlers survive, and Holden, Amos, Murtry and Lucia (Rosa Gilmore) – who saw and felt the same things Holden did when he was between spaces – are rescued by Alex and Naomi aboard the Roci.

Holden informs Chrisjen (Shohreh Aghdashloo) that everything will be fine, and that the most dangerous things on the planet will be the things humanity brings with it.

Cibola Burn was written by Abraham, Franck and Naren Shankar, and ties up some loose ends while starting a number of new threads.

On Mars, Bobbie (Frankie Adams) discovers that elements within the Mars navy and police forces are working with the Belters, specifically the new threat of the series, Naomi’s ex, Inaros (Keon Alexander), who has absconded a couple of interstellar rocks to drop them down the well, on Earth.

Bobbie reaches out to Chrisjen as well, who has just lost the Attorney-General position she was trying to hold onto, and suggests the two of them working together to find out what is going on. Meanwhile, the new AG has promised to open the rings and the worlds beyond to all who would travel there.

Naomi reaches out to Fred (Chad L. Coleman) to ask for the favor owed her, help her find Filip (Jasai Chase Owens) the child she had with Inaros.

But it looks like Asford (David Strathairn) finds him first, and it costs him as father and son prepare to wreak destruction in the Sol system in the name of the Belters.

Phew. That’s a lot. Happily, I don’t have to wait a year to find out what happens next, I can dig into Season Five of The Expanse next week!