Spoilers for Game of Thrones, season 7 below.
Winter has arrived on Game of Thrones, and Sansa and Arya Stark's reunion at Winterfell is turning icy pretty fast. There's already conflict between them, and now sneaky Littlefinger is trying to pry the rift open further.
At one point during "Eastwatch," Littlefinger procures a note from Maester Luwin’s extensive archives. From the way he's sneaking around the castle, it seems pretty clear that he doesn't want anyone to know that he has it.
So then Petyr Baelish goes and hides the note, but (surprise!) Arya is determined to find out what it says. And after a quick search of Littlefinger's chambers, she finds it, hidden in his mattress.