Zarc

The episode is called " Eastwatch " , so many events will took place there. 

On the trailer , Bran has a vision of the army of the Night King approaching the fortress. We should see Tormund and his mens alongside the night's watch. 

On his side , Jon will receive the information from Winterfell and will surely decide to go to Eastwatch. By the way , we see on the trailer that drogon look pretty fine ( i'm pretty sure that when we see Daenerys approaching Jon with drogon , something will happen... due to Jon's true origins. 

Another information : it's possible that we finally see Gendry again ( Robert Baratheon's bastard ).

If we remember the main trailer of the season 7 , we saw a small group surrounded by the Night King army. We don't know exactly who , but pretty sure it will be Jon with Tormund , Sandor Clegane , Beric Dondarrion ( fire sword ) , Thoros of Myr , and probably Gendry too. 

It will be very georgous if we end this season by : they are surrounded and have no chances to survive ( i think Thoros or/and Beric will die )  , and at the last moment Daenerys come with her dragons to save them , and we should arrive at this epic conclusion :

What we should expect ? One of Daenerys dragon will obviously die and be turned into an ice dragon , or.... a 4th dragon already exist ? hummm.