“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 Robertâ€™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 Kingâ€™s Landing, swear fealty to King Joffrey and prevent any strife between the great houses of Lannister and Stark.”

This post containsfor Sunday night’s Game of Thrones , so if you haven’t seen the episode yet and want to avoid them you might want to become “no one” instead of continuing. Littlefinger ‘s plan to divide the Stark children came into greater focus Sunday night, when he set a trap for Arya to find an incriminating letter Sansa once sent her brother. But while his schemes have always succeeded thanks to his ability to sell a lie, Littlefinger has no idea they won’t work on Arya . That’s because she was trained by the world’s best deceivers how to play the lying game. Last week we were concerned with Littlefinger’s grand scheme and how it related to Bran , that Valyrian steel dagger, and Jon. Now we know he also has has the same plan in mind for Ned’s daughters, because Baelish doesn’t just need the Stark children divided, he needs them dead.While he was working his devious magic with that dagger, he saw Arya go toe-to-toe with Brienne. However, rather than Arya being a skilled warrior posing a problem for him, it presents an opportunity. What do you do if you have a trained killer and need dead Starks? You combine the two.The letter Baelish had the consistently overwhelmed Maester Wolkan deliver to him was the letter Cersei had Sansa write to Robb way back in season one, in which Sansa implored Robb to bend the knee because Ned had committed treason.Here’s what the full letter says:

Out of context it’s horrible, making Sansa look like she was siding with the Lannisters while her father was in chains. Considering she then married Tyrion, it’s not a great look.

But just like she was forced to marry Tyrion, Sansa was forced to write that letter. When Robb received it Maester Luwin understood exactly what it was about. “It is your sister’s hand, but the Queen’s words,” he told Robb.But there’s no way for Arya to know that, no context to explain why Sansa wrote it. Not to mention that letter was written shortly after Sansa had betrayed Arya, when Sansa lied about what happened with Joffrey and Arya on the King’s Road. Sansa’s lie led to both Mycah the butcher’s boy and Sansa’s direwolf Lady being killed, as well as Arya having to send Nymeria away. Arya hated Sansa for what she did that day, so finding “proof” that Sansa had betrayed her family once more in her quest to become queen rings true.Especially when in this same episode Arya correctly called Sansa out for 1) not defending Jon, 2) worrying more about working with allies than her family’s honor, and 3) thinking about her own future as ruler in the North.It was another master stroke by Baelish. He makes Arya turn on her sister, which could result in one or both of them dead. He doesn’t attack the pack, he gets the pack to turn on themselves.But the way Arya was able to read Sansa’s mind and know she was lying is the same reason Baelish’s plan to manipulate her is doomed to fail, because Arya wasn’t just trained by the Faceless Men to kill, she was trained to know when someone is lying.All of that time spent sitting and getting whacked by Jaqen and the waif while playing the lying game were part of her training too. The Faceless Men are not only experts at deception, they are world class experts on rooting it out, a skill Arya was taught many times.No matter how good Baelish is at lying he has not only found his match, he’s found his better.That means there are two distinct possibilities for what happened in “Eastwatch.” The first is that he successfully tricked Arya into thinking Sansa betrayed her family, but Arya will find out the truth eventually, especially if she confronts Sansa. That would ruin his plan and likely lead to him being dead, but it does leave open the chance for real discord between the sisters, which could then lead Sansa to turn on Arya before Arya figures it all out.The second possibility though is far more enticing. That’s because there’s a chance Baelish didn’t play Arya at all, but instead she played him.When Arya was spying on Baelish she secretly watched him speaking to a young informant, but look at where Aryastanding.Arya didn’t attempt to stand in the shadows, she stood in the light, right in his peripheral vision. A step to the left would have concealed her entirely, which makes her standing in the light remarkably dumb for a person trying to be covert. You don’t have to be trained at the House of Black and White to know how to hide in the dark.This is the best evidence of her doing that intentionally, exactly so Baelish would see her. Arya wants Littlefinger to know she doesn’t trust him, but that only works if he thinks she’s too stupid to keep it a secret.With her trap laid, he then did exactly what she expected, which is try to come between her and her family. But for all of her changes, she ultimately left the Faceless Men because she is Arya Stark of Winterfell.And she didn’t come home to turn on her family.Littlefinger’s latest plan is as good as any he has ever devised, but unfortunately for him it won’t work on someone trained to identify liars. Sansa wrote that letter, but she didn’t betray her family, and if Arya doesn’t know that already she’ll figure it out.And then her other training will finally mean the end of Baelish’s schemes forever.What do you think? Who was playing whom last night, and who will come out on top? Give us your predictions in the comments below.For more Game of Thrones theories, check out our look at the Rhaegar revelation , why Littlefinger gave Bran the dagger in the first place, and our panel discussion of all things “Eastwatch.”[brightcove video_id=”5541062809001″ brightcove_account_id=”3653334524001″ brightcove_player_id=”rJs2ZD8x”]

Images: HBO