On the season six finale, Arya disguised herself as a servant girl (using Faceless Man magic) and killed Walder Frey. But before murdering him, she killed his two sons and had them baked into meat pies that were then fed to Walder. 

So what is her next move? The remaining people on her list, Cersei Lannister and the Mountain, are south. But maybe she'll hear that Jon and Sansa are back north and ride for Winterfell?

Also last we heard, Edmure Tully (the brother of Catelyn Tully and lord of Riverrun) was being held prisoner at the Twins. What will come of him?