The DLC is called Rise of the Deliverance, and it basically tracks the formation Deliverance after King Lima's death. It's heavily centered around Clive and Fernand, and also expands significantly on the rest of the Deliverance (Mathilda, Clair, Lukas, Forsyth, and Python). In addition to the 4 chapters that it contains, it also unlocks a plethora of supports for the main characters that are generally of really high quality and absolutely should have been included in the main game. It also unlocks a few new Memory Prisms. If you're planning on buying any Echoes DLC, this one is definitely the one to get IMO. Alternatively, you can just watch a playthrough of the DLC on Youtube, which I highly recommend you do if you don't get the DLC yourself; trust me, it's well worth your time, and it really fleshes out the Deliverance characters.