Here is an overview of the trailer, via Activision:
Destiny 2: Forsaken opens with an explosive jailbreak in the Prison of Elders. As the most notorious outlaws in the system escape their confines, the only thing standing between them and our home is you and Cayde-6, the most legendary Hunter sworn to protect the City.
A Vanguard doesn’t go down without a fight. Witness Cayde’s last stand.
Watch the trailer below.