This is Book 4 of a series set at Starbase 47, aka Vanguard. The series takes place during the same time as the original Star Trek's five-year mission. But Stark Trek: Vanguard is much more than a TOS DS9. For starters, the starbase has a number of starships assigned to it at all times, so you have not only the cast of Starfleet officiers and civilians that work and live at Starbase 47, but the crews of the starships as well.
The thing I really love about series like ST:V is that almost none of the characters are bulletproof. The three exceptions in this case are Dr. M'Benga, who hasn't yet transferred to the Enterprise, T'Prynn, who shows up in later Star Trek: The Lost Era books (although after what was happening to her in this book I was starting to wonder if I had my timeline mixed up), and Admiral Nogura.
Admiral Nogura's previous Star Trek history is only as a reference in Star Trek: The Motion Picture; he's obviously Admiral Kirk's superior, and obviously a tough leader, but that's all we know. Here we get to see that legend built as he takes command of Starbase 47.
Vanguard continues to be full of surprises and big changes.