When Belleger discovers that it no longer has the gift of sorcery available to it, not only do they realize that Amika has a severe advantage over them, but even their standard day-to-day activities are adversely effected. Without magic, processes they've come to depend on will not work. And, then, there are also the rifles. The one advantage Belleger had against Amika was their rifles, but they have too few and, without the Decimate of Fire, are unable to make more.
After discussion, it is determined that there is a Decimate beyond the six commonly known ones; a Seventh Decimate, which can prevent sorcerers from being able to use their abilities. Amika must have used the Seventh Decimate against Belleger, robbing them of all magic. Fearing that Amika's next attack could be their final blow against Belleger, Prince Bifalt is sent, along with a small party, to seek out a mysterious sorcerous library believed to exist in the wastelands of the desert. Prince Bifalt would do anything for his country, but he has misgivings about his quest, in part because he has a secret. He has been magically saved from certain death on the battlefield, after which a voice in his head asked, "Are you ready?" For what, he does not know, but he fears that he might be used against Belleger if he isn't careful. As he undertakes his quest, he will discover the world is much larger than he ever imagined and he'll have to come to terms with that.
While I do, wholeheartedly, agree that this book sets the story up to be continued in the next book, I don't feel that excuses the book from being a good, standalone story. Instead, I found Prince Bifalt to be generally unlikable and his closed-mindedness and shortsightedness to be difficult to cope with. He comes across as a very two-dimensional character throughout the book and his behavior at the very end of the book seems less like the result of gradual character development, throughout, and more like a change to the character that was imposed onto the story to set up the desired premise for the next book. The adventure, itself, is interesting, as are the different characters they meet along the way, but Prince Bifalt almost seems to strive to be irredeemable.
Seventh Decimate feels like an introduction to a series and not much more. If you're not completely sold, I don't blame you. I would suggest waiting to see how the next book fares before investing in the series.