In Episode 6, the reports have it that it shall be Walder Frey of Essos who shall be featured. As the architect of the Red Wedding that caused the death Catelyn Stark and Robb Stark and the latter’s pregnant wife, Walder Frey is due to be exacted vengeance upon by Jon Snow and Sansa Stark and it looks like it would happen that way.
The Episode 6 synopsis said that it will feature the return of an old foe. The same synopsis also says that Gilly shall finally able to meet Sam Tarly’s family. Over at Braavos, Arya Stark will face a difficult choice. And over at King’s Landing, Jamie Lannister will finally face off with the High Sparrow.
Episode 7 is entitled “Broken Man” and its synopsis reads that the High Sparrow is eyeing another target even as Jamie confronts a hero. Arya will be making a plan even as the North is reminded.
It appears that it would be in the seventh episode where Jamie Lannister will face off against Septon Meribald.
There are also rumors that it could be the return of the Blackfish. As to how the North would be reminded, it seems that the white walkers will once again drumbeat their attack on the North in preparation for the coming of winter.