Episode nine of this season of Game of Thrones is titled, “The Rains of Castamere,” but just what the heck is that? Believe it or not, it’s a song!

“The Rains of Castamere” essentially serves as the Lannister family theme song. It represents the victory of Lord Tywin Lannister over House Reyne of Castamere in a war preceding the events of the show. Never heard of House Reyne? That’s because they were completely wiped out by the Lannisters, so the song serves as a warning to all who would dare defy the Lords of Casterly Rock. Here are the lyrics:

And who are you, the proud lord said, that I must bow so low?

Only a cat of a different coat, that's all the truth I know.

In a coat of gold or a coat of red, a lion still has claws,

And mine are long and sharp, my lord, as long and sharp as yours.

And so he spoke, and so he spoke, that Lord of Castamere,

But now the rains weep o'er his hall, with no one there to hear.

Yes now the rains weep o'er his hall, and not a soul to hear.

Sound familiar?  “Rains of Castamere” played twice in Season 2, Episode 9: “Blackwater." The song was first sung by Bronn, who sings the song while drinking and partying with the City Watch before the battle begins. It plays again after Stannis and his men were defeated at the Battle of Blackwater Bay. (You can listen to The National sing the Lannister song here.)

Then in Season 3, Thoros of Myr was singing it when Arya first encountered The Brotherhood Without Banners back in Episode 3. Does that mean The Brotherhood are in cahoots with the Lannisters? Or does it just mean that it’s a catchy song? Whatever the implications, we’re guessing episode nine has some trouble in store for the enemies of mighty House Lannister!

So why is Season 3, Episode 9 called “The Rains of Castamere?” Well, it probably has something to do with a huge Lannister victory. For those of you who have read the books, we’re assuming it’s the Red Wedding.

Get more Game of Thrones spoilers here.

Catch the next episode of Game of Thrones Sunday, May 19 at 9 p.m. ET/PT on HBO.