The story in NF take place a few years after chapter 1 and 2. In Nightfall, there is a new bad guy in town. And the leader of an elite warrior group, protector of elona, The Sun Spear, has come to ask for aid from the heroes who defeated Shiro and The Lich Lord.
Yeah it's in the name of the game, if the evil win, night will fall,.....foreverrr!
Oh and this chapter is the closing chapter in the trilogy as well, you won't be blowing up the second deathstar sadly. But you will learn alot about the bad guys from the earlier chapters, why they did what they did and what happen to them after you finished chapter 1 & 2.