Horizon Forbidden West is almost out, and it basically picks up exactly where the previous game left off. The opening hours will pelt you with strange names, supposedly familiar faces, and a helpful but extremely brief recap of the events of Horizon Zero Dawn. If you’re planning on jumping into the new game or you’re just wondering why, for example, robot dinosaurs roam its vast and beautiful world, here is a crash course in everything you need to know.

Horizon Zero Dawn was a big game steeped in sci-fi jargon, exposition, and background lore. Much of this worldbuilding was also relegated to audio logs and collectibles, as well as the game’s post-launch expansion, The Frozen Wilds, making it easy to miss. Even if you played the game back when it was released in 2017, I promise you you are going to want a refresher. And if you skipped Horizon Zero Dawn entirely, well, you might want to go back and fix that, but if not, the below rundown should have you covered.

The heady concept behind Guerrilla Games’ open-world sci-fi series is that in the year 2048 a tech bro named Ted Faro created militaristic machines that could self-replicate and consume biomass for fuel. With the planet facing refugee crises and civil unrest due to global warming, the machines were used to put down protests and protect those in power.

This line of robots, called Chariot, supplants every major army in the world, and then, obviously, glitches big time (for mysterious reasons, of course), threatening to wipe out all life on the planet in an endless cycle of resource exploitation and reproduction. This menace becomes popularly known as the Faro Plague.

At this point the scientist Elizabet Sobeck, Faro’s former business partner who split after she realized he was more interested in military contracts than fixing the environment, comes up with a solution called *ominous pause* Project Zero

What was Project Zero Dawn?

Instead of trying to save humanity, Sobeck decides to preserve it through a complex series of AI programs called GAIA. This friendly computer will 1) eventually hack into the robots and shut them down, 2) terraform the planet and restore nature and 3) repopulate the earth with clones once everything is ready.

GAIA has nine, count them nine, subordinate functions. One of these, MINERVA, was in charge of hacking into and eventually disabling the Chariot drones. Another was HEPHAESTUS which would create brand new machines modeled after nature to help fix the planet and take care of the new humans. (Why do so many of these new machines look like dinosaurs? No reason really other than Guerrilla Games thought it would be cool). A third was APOLLO, in charge of storing humanity’s collective knowledge and teaching it to the new humans. Finally there was HADES which was responsible for killing everything on the planet and starting the process over from scratch if things went sideways.

Before Project Zero Dawn can be completed, Sobeck sacrifices herself to buy the team working on it extra time. Faro goes haywire himself and destroys APOLLO because he thinks the new humans will somehow be less flawed if they remain ignorant of their past. He also kills the rest of the scientists once Project Zero Dawn is complete.

What went wrong with Project Zero Dawn?

If things had worked out there would not be a Horizon Zero Dawn, let alone an entire series, but by the early 31st century it seemed like everything had gone according to plan. That is, until a mysterious signal was beamed into GAIA granting each of its subordinate AIs sentience, including HADES. GAIA blows up the Project Zero Dawn facility to slow HADES down but it infects GAIA with a virus to free itself and the other subordinate AIs. In response, GAIA uses one of the remaining Project Zero Dawn incubation facilities to create a clone of Sobeck and leaves it on the doorstep of the Nora tribe (An incredible Hail Mary for a super computer capable of running an entire planet). The clone grows up to be Aloy, Horizon’s central hero.

To destroy everything, HADES begins corrupting the world’s caretaker robots with the ultimate goal of rebooting the dormant Chariot machines from the Faro Plague. HADES also enlists the help of a mysterious wanderer named Sylens who’s thirsty for knowledge from the past and convinces a splinter group from the Carja tribe called the Eclipse to worship it like a cult. Aloy ultimately thwarts all of their plans in a final showdown with HADES. Instead of HADES being destroyed, however, it’s captured by Sylens with the intent to learn more about humanity’s history and who or what caused HADES and the other AI to go haywire in the first place.

Spoiler Warning: If it wasn’t already obvious, this post will be full of spoilers for Horizon Zero Dawn and The Frozen Wilds.