This post contains frank discussion of Season 7, Episode 5 of Game of Thrones: “Eastwatch.” If you’re not caught up or don’t want to be spoiled, now would be the time to leave. Seriously, I won’t warn you again. Skedaddle.

In a jam-packed episode filled with historical revelations, the potential doom of Cersei Lannister, dragon interactions, and returning favorites, we might want to spend a few minutes considering that mysterious raven scroll Arya uncovered.

Back in Episode 3, we learned that despite many invasions and a destructive fire in Season 2, Winterfell still has a very impressive records room. Maester Luwin, it turns out, kept a copy of every single raven scroll ever sent to King’s Landing, and that fact didn’t escape Littlefinger’s notice.

So he’s now deployed something poor Sansa wrote under duress back in Season 1 against her in an attempt to drive a wedge between the Stark sisters. He has good reason to know the letter existed in the first place; he was in the room when Cersei forced Sansa to write it. “The girl is innocent, your grace,” Littlefinger told Cersei after Pycelle implies that Sansa should be thrown out on her ear or worse after Ned Stark is arrested. “She should be given a chance to prove her loyalty.” That chance, it turns out, took the form of the letter Arya found—which, in the books, is sealed and sent on its way by Lord Varys himself. (For shame, Lord Varys.)

Cersei urges Sansa to write to her mother and brother saying: “If you would help your father, urge your brother to keep the king’s peace.” Sansa asks of her father: “What will happen to him?” The Queen replies, smoothly, “That depends on your brother and”—holding up a quill—“on you.” What’s a poor, pressured girl to do?

In this week’s episode, an already-suspicious-of-Sansa Arya reads the damaging letter Littlefinger planted for her to find:

Robb, I write to you with a heavy heart. Our good king Robert is dead, killed from wounds he took in a boar hunt. Father has been charged with treason. He conspired with Robert’s brothers against my beloved Joffrey and tried to steal his throne. The Lannisters are treating me very well and provide me with every comfort. I beg you: come to King’s Landing, swear fealty to King Joffrey and prevent any strife between the great houses of Lannister and Stark.

For what it’s worth, back in Season 1, Robb (with the help of Maester Luwin) was able to see that Sansa wrote the letter under duress.

And the letter did not have its desired effect; in fact, quite the contrary. Robb called his Northern bannermen to rally against Joffrey immediately after reading Sansa’s message. But Arya doesn’t know any of this—and, to her slight credit, the earlier version of Sansa was always fairly terrible to her younger sister. In the letter-writing scene in George R.R. Martin’s novel, Sansa tells Cersei: “I’m not like Arya. She has the traitor’s blood, not me. I’m good.” It wasn’t a good look back then, but both girls have come a long way since. If Littlefinger could just stop interfering, they might be able to figure that out.

In the post-episode interview, showrunner D.B. Weiss explains Littlefinger’s scheme:

[Arya] gets roped into spying on somebody who is actually leading her by the nose. He’s looking for a way to prevent this sister bond from developing further, because the tighter they are, the more definitively he is caught on the outside of it.

On the Sansa end of the relationship, he’s seen the opening, and now all he needs to do is give Arya a cause to display real rage towards Sansa. He knows full well that with what’s going on in Sansa’s head with regards to Arya and how dangerous she is, when Arya starts to act dangerous and act angry, he knows where Sansa is going to turn.

Let’s hope Sansa (and Arya) are smarter than Littlefinger is giving them credit for.