This is our Game of Thrones Season 7 Episode 2 prediction break down from that very very short trailer seen below
The trailer opens with "A Targaryen Can Never Be Trusted" as a lord directs this comment to Jon Snow. Most likely this is right after Winterfell learns that Daenerys has taken over Dragonstone. Jon Snow is seeking Dragonstone and well, the mother of dragons has quite the fair share of the material. We know Jon and Daenerys will meet up, this is my guess on what will bring the two together.
We see the return of Yara and Theon Greyjoy. The remaining Greyjoy family that hasn't been murdered or betrayed on by Euron. Here, she mentions of attacking King's Landing. We also see a scene with Ellaria Sand and Yara enjoying a kiss, did Ellaria Sand just kill Yara. Since we did see a scene where Euron wants to bring Cersi a gift, either to eliminate House Martell or well, join up with Cersi.
The scene where Arya meets a wolf, we can assume that is a direwolf and can only be Nymeria. The one where she releases to protect her. If this is the case, then a great reunion is about to happen. Score one for House Stark once again!
With all that, what do you guys think will happen in Westeros come Sunday. Episode 2 is titled Stormborn and the preview really does focus a lot on the Daenerys and everyone around her.