The third part is titled "The Sword in the Darkness" and Telltale has released a quick story summary of what to expect in this episode:
Asher, the exile, heads to Mereen in search of an army to take on the Whitehills. Meanwhile, far across land and sea in Westeros, Mira must deal with the lethal politics of King's Landing. Her family's safety is paramount and she will do anything to protect them, but nothing is given freely, and her choice of allies may soon come to haunt her. To the north, in Ironrath, the Whitehill occupation continues. Gryff Whitehill, fourth-born son, is out to prove himself, and brutality and violence grows daily, pushing the Forresters to make far-reaching decisions. Finally, at the Wall, Gared learns that he must head north if he is to help his house survive. But fate is cruel, forcing choices that will change his path forever.
There's also a new gameplay trailer that shows some sword fighting action and even a quick glimpse of a dragon at the end. The first episode is free, while the second is $4.99 for the Xbox One and Xbox 360. You can also purchase all six episodes for a total of $24.99. PC owners have to pay $29.99 up front to get all six episodes as they are released.
Source: Telltale Games