Both the capabilities and controls of the speedlights that make up the Nikon Creative Lighting System are substantially different from the flash units offered by other manufacturers. It's true that the manuals that Nikon includes with these units are quite comprehensive, but the print is small, the text not always clear, and applications not always apparent. It makes sense to offer a book that explains the use of this system to photographers, especially those encountering the system for the first time.
After an introduction that offers the standard but useful introduction to the nature of light, Zettl describes several of the flashes and cameras that make up the system: e.g. the SB-900, SB-700, and so forth. There is a section on setting up the menus on these units, which is always a little confusing to photographers, especially newcomers. The author then discusses light modifiers and lighting patterns and techniques like bounced flash and fill flash. There is a chapter on off-camera flash, including the use of multiple speedlights. She finishes with a review of several photo shoots, explaining how she used flash to enhance the images.
This is an excellent introduction for the new speedlight user who can easily be intimidated by these units. The author even makes reference to certain details that are often overlooked by other authors, like the use of the SG-31R device on cameras with built-in flash used only as a commander.
I wish there had been more material. To start with, the most powerful flash unit described is the SB-900, even though by the date of publication, Nikon was producing the SB-910. Luckily the improvements to the unit were internal, but the controls seem to be just about the same. The book also fails to address some of the older units that are around, that still offer many capabilities that can be integrated into the system, like the SB-800. On the other hand the owners of these older units probably understand how they work by now.
I would also have liked to have seen a description of the use of multiple flashes in modeling portraits, showing the use of the speedlights as main, fill, hair, and so forth. On the other hand that much information might have been too much for the new speedlight user. Ultimately, the photographer who expects to get the most out of his or her speedlights will have to read other books that explain these uses.
The experienced user of speedlights will probably not find anything new here. On the other hand, those just acquiring the first advanced speedlight will find more than enough information to begin using it effectively.