After a two-year wait, everyone's favorite fungal zombie apocalypse show is finally back: The second season of "The Last of Us" premieres Sunday.

Created by Craig Mazin and Neil Druckmann, HBO's acclaimed survival drama is set in a world that has been ravaged by the outbreak of a mysterious mutant cordyceps fungus that turns human hosts into horrific, mindless monsters. An adaptation of the hit video game of the same name, the nine-episode first season followed gruff smuggler-turned-surrogate father figure Joel (Pedro Pascal) and his teen charge Ellie (Bella Ramsey) on a cross-country journey to help find a way to save the world. Ellie's immunity to the fungus potentially holds the key to a cure.

Here's everything you need to know about Season 1 before diving into Season 2.

How did the apocalypse happen?

In the world of "The Last of Us," a mysterious cordyceps outbreak in 2003 devastates humanity. Those that are infected transform into zombie-like hosts that exist for the sole purpose of spreading the fungal infection to others. The longer they are infected, the more monstrous their appearance becomes.

Twenty years later, society has collapsed and survivors in America are left to live in military government run quarantine zones controlled by FEDRA (the Federal Disaster Response Agency) or former QZs that were liberated from the oppressive agency. There are also settlements that independent communities have established on their own — as well as survivors that choose to stay more isolated.

Who are the key players?

The first season introduces audiences to Joel Miller, a contractor living with his teen daughter Sarah. Sarah is killed by a soldier during the chaos of the outbreak while Joel was trying to get them to safety. He never really recovers from her loss.

By 2023, Joel has lost touch with his brother, Tommy, and is a smuggler working jobs out of the Boston quarantine zone along with his partner Tess. After a deal goes awry, Joel and Tess meet Ellie, a teenager being held captive by a rebel militia group called the Fireflies. The leader Marlene asks Joel and Tess to smuggle Ellie out of the city in exchange for supplies.

Ellie, it turns out, is immune to the cordyceps infection and Marlene has planned for her to be transported to a group of Fireflies out west in hopes of creating a cure. (Ellie's immunity likely stems from her mother becoming infected just before giving birth to her.)

Were they successful?

Not quite! The handoff never happens because the Fireflies who were meant to escort Ellie across the country get infected before their rendezvous. Tess is also a casualty. So Joel and Ellie set off to find the other Fireflies on their own.

The two grow close over their perilous journey as Joel and Ellie encounter plenty of monsters and monstrous people. But they also cross paths with Tommy, now married and living in the peaceful settlement of Jackson, Wyoming.

Joel and Ellie eventually make their way to Salt Lake City, where the teenager is taken to surgery to begin the process of figuring out a cure. But when Joel learns that the procedure will kill her (the doctors need her brain), he goes on a deadly rampage to stop the Fireflies and escapes with Ellie. As they head back to Jackson, Ellie asks Joel what happened and he tells her that the militia group had already unsuccessfully tried to develop a cure with other immune people and had given up.

What's next? (No spoilers)

This season is set to pick up a few years after the events of Season 1. Ellie and Joel have been living as productive members of the community in Jackson. Among the new characters to be introduced are Dina (Isabela Merced), Jesse (Young Mazino) and Abby (Kaitlyn Dever).

How about some spoilers?

Season 2 and beyond will be adapting "The Last of Us Part II." Those familiar with the events of the video game know to expect some romance, angst, death and a whole lot of revenge. The game also introduced different factions of people who live very different lives from those in the community at Jackson. There's also a bit more that could be introduced about the types and behavior of the infected.

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