The book is a prequel to Riyria Revelations. Basically it is a story of how Hadrian and Royce met and the reason they became known as Riyria (which means two in Elven). There were quite a few bits of information regarding early Riyria history in Riyria Revelations, so readers familiar with it will not find great surprises in the overall plot. The subplots are different matter though.
In the first chapter of the book Hadrian came back to civilized lands from south where he fought gladiator battles in the arena. He finally got fed up with this business, but he really has no clue what to do with his life anymore. The next chapter switches to Gwen whose POV makes up almost half of the book.
The first thing I noticed about the book is that the beginning is much darker than the first book of the original series. The latter starts with established duo teaching highway robbers how to do their jobs properly; the former shows a gruesome murder of a prostitute (Gwen's chapter). The banter between Hadrian and Royce was half of the fun in the original series. Given that these guys officially meet way into the book, the banter is absent for quite some time.
The original series evolves from some local jobs done by Riyria into a tale of epic quests, Empire-wide conspiracy, grand magic, and a search for a missing heir. This one does not have any epic feel; this is just a story of two completely different guys who also hate each other learning how to work together.
I already mentioned that the beginning is kind of slow. Once the story finally gets rolling, it gets really exciting, I-do-not-need-no-sleep level of excitement. There are some very nice and unexpected plot twists along the way with the biggest one happening in the last chapter.
The final rating for the book is solid 4 stars.