This is, perhaps, more "technical" than some of the other books, as Don Juan spends much of the book trying to get Carlos "up to speed" as the new Nagual, putting him through various exercises to shift his "assemblage point" and move through various levels of existence as needed, in preparation for such time that he'd be on his own. The main test at the end (referenced in the previous book) is Castaneda and a couple of the other warriors of his party having to jump off a mountain cliff "into an abyss", the test being, of course, in that they must bodily shift into an alternative reality to avoid being killed by the fall (all of them survive).
Again, having studied some analogous traditions, I find the details of these things fascinating, and there is quite a lot to absorb along these lines in both of these books. This one also gives yet another version of Don Juan's teacher, the Nagual Julian, from Don Juan's perspective, as opposed to the story told Castaneda in the earlier book. Don Juan also discusses how their lineage developed, based on the ancient sorcerers (the "Toltecs", one of whom, a "death defier" was still actively linked to them), but diverging into a new understanding.
I was also quite interested in something that dove-tailed with other traditions about "God", such as that dealing with Metatron ... in this Don Juan insists that what humans see as "God" in mystical, spiritual, and religious experiences is simply "the Mold of Man", the template (somewhat ala one of Sheldrake's morphogenetic fields) which assembles us on this plane. An "emanation of the Eagle", it is perceived by seers as divine, but is simply the "perfected image" of our own state of being ...."the mold is our God because we are what it stamps us with and not because it has created us from nothing and made us in its image and likeness" ... it is simply human self-centeredness that dresses this up in the trappings we've invented for divinity and calls it "God".
The problem with being the seventh book in a series, is that (to a greater or lesser extent), the book is necessarily based on its predecessors. While I, having had read all the previous books at various points (and studied similar traditions) can "get" much of what is going on in The Fire from Within ... and while I would love to heartily recommend this and The Eagle's Gift ... that rave has to come with caveats that a reader unfamiliar with the "Castaneda universe" is likely to have a hard time in absorbing what's going on. That said, this is a rather remarkable book, and I'm certainly glad to have it in my collection! Again, this is still in print, so you should be able to find a copy at your local book store, but you can find it in the hardcover edition (what I picked up) for under a buck via the Amazon new/used vendors.