Fifth in a series of six
It all comes back to Travis. His travel to the past made it so that one of the Stones of power was in two places at once. That opened up a rift that allowed the dark god Mohg to influence Earth. That also brought Jack Greystone to Castle City, where he would later befriend Travis, and make him a runelord, one who would become the prophecied Runebreaker, the one to destroy the world...
Of course, Travis doesn't want to destroy the world. He'd settle for destroying Duratek, except that he's out of resources and is homeless at one of the coldest times of the year in Denver. And it's a bit hard to come up with a good plan when you're cold and hungry.
Grace isn't much better off. She's in charge of the defense at Gravenfist Keep, the best point to defend from the Pale King's assault. However, the bulk of the force may not get there in time, and though she has the key to the keep's magical defenses, she has no idea how to use it.
Anthony has a way of putting in absolutely ludicrous moments that set the scene precisely. My particular favorite is a group of stalwart knights wandering around a forest, sniffing the trees... because Grace just said that they smelled like butterscotch, and they're curious to see what she meant.
Everything comes to a head in this book. The prophecies get fulfilled, the battles get fought, the visions come to fruition. And yet this is not the last book in the series...