Upon reaching the second threshold on the Satan’s Wrath meter, there will be a short cutscene and then this mission will begin. You have to rescue all of the major power players in Hell, who have been kidnapped by Satan’s forces. Each one is being held by some Dark Inciters and killing those, then reviving the characters will rescue them.
There isn’t too much else in the way besides the Dark Inciters, but be careful of stray demons that might join the fray. Of course, the Inciters can throw grenades at you that strip you of your powers while you’re in its blast radius, so be on the lookout for the grenade icon. The mission is over when you rescue all five.