One year after Gorrog was defeated, Hell has returned and a new demon has brought back Gorrog from his sleep,

Kingdoms all around Equestria feel the Black Tide as it emerges from Hell, its strength soon shall be put to the test as the survivors of the First Demon War prepare for a far larger assault, as Hell returns with a vengeance.

(This story is the sequel to Equestrian Doom, you can read it but I'll try to make it understandable for those who haven't.)