HBO’s Game of Thrones is a dense series with a huge weight of history behind its story, so in practically every episode, something happens that could use a little explanation. So every week, The Verge will be diving into a scene or event from the latest installment of the series and explain how we got here. Whether you’re basically a Game of Thrones maester or you need a little reminder about previous events, we’ll try to help you keep your history straight.

Game of Thrones is in full swing now, and after a relatively sedate opening episode, things kicked off with a bang this week with “Stormborn.” This week, for our dive back into the dusty stacks of series’s history, we’ll be looking at the infectious disease of greyscale.

Spoilers ahead for Game of Thrones season 7, episode 2

Jorah’s greyscale infection

One of the bigger foci in tonight’s episode was on Jorah Mormont’s developing greyscale infection, which was teased last week in one of our favorite scenes. Jorah was infected with the disease while defending Tyrion back in “Kill the Boy” (season 5, episode 5), while the pair was traveling through the ruins of Old Valyria. Jorah tried to hide his infection for a while, but it was discovered at the end of last season, and Daenerys sent him away to find a cure. (Not to be confused with his first exile for betraying her back in “The Mountain and the Viper” in season 4.)

What is greyscale?

The show doesn’t delve too deeply into what greyscale is or where it comes from, but if we turn to the books (specifically, A Dance with Dragons and The World of Ice and Fire), we can find out a little more. There, greyscale has the mythical origins in an event known as “Garin’s Curse,” where a Rhoynar prince named Garin called down a plague upon the Valyrian conquerers who tried to enslave his people. Whether that holds true in the show, or the disease is considered to have a more conventional medical explanation, remains to be seen.

Shireen Baratheon, the lone survivor

Over the course of Game of Thrones, we’ve already met a greyscale survivor, one who’s mentioned in this episode — the late Shireen Baratheon, daughter of Stannis Baratheon. Shireen is infected by a doll Stannis purchased from a Dornish merchant, and the disease begins to affect the left side of her face. Stannis — in perhaps his single redeeming speech — noted that he chose to find a cure for Shireen because she was his daughter, instead of dooming her fate to join the stone men in Old Valyria. (Stannis then burns her alive at a stake to try and win a war, so… yeah. Less heartwarming there.)

Stone men

The “Stone Men” (and women) are a group of people infected with greyscale. The disease turns victims’ flesh into the horrific gray scabs that give the disease its name, but it doesn’t kill quickly; as noted in this week’s episode, Jorah could expect to live another decade or two. What greyscale does is ravage the mind, leading to the bestial colony of outcasts that attacks Tyrion and Jorah when they attempt to pass through the ruins. Jorah was sentenced to join those damned souls or commit suicide, which is why Sam is willing to hurt him so badly in the attempt to save him.

The cure?

Sam refuses to let the son of Jeor Mormont — the 997th Lord Commander of the Night’s Watch, and his mentor — go down without a fight. (Sam briefly served as Mormont’s steward at the Wall before his death, and found him a more respectful father figure than Sam’s own father, Randyll Tarly, who sent him to the Wall in the first place.) Sam finds a possible cure in the books of the library in the Citadel, but Archmaester Marwyn tells him the cure is too dangerous, and that the last maester to try died of greyscale. This being Game of Thrones, Sam attempts the cure anyway, slicing off Jorah’s infected tissue in one of the least visually pleasant scenes we’ve had on the show since Sam’s chamber-pot scene last week.

It’s worth noting that this doesn’t seem to be the same cure that was applied to Shireen, who still bore the “scales” of greyscale. It seems her case was cured by a different method, which the show addresses quickly. Archmaester Marwyn shoots down Sam (and the legion of theorizing fans) by noting that Shireen and Jorah’s cases are very different levels of infection in two individuals of drastically different ages.

We’ll have to wait until later in the season to find out whether Sam’s horrific cure is successful, but given that Jorah is an important character in the show, I’d bet he lives — at least long enough to matter in some way to the plot. Then again, this is Game of Thrones, which is notorious for its surprise deaths of plot-significant characters, so at this stage in the game, who knows?

Correction: Jeor Mormont was the 997th Lord Commander of the Night’s Watch, not the 998th.

Learning Game of Thrones theme song on a futuristic keyboard