This is book two in the Deep Space 9: Mission Gamma series.
The Defiant is off exploring the Gamma quadrant, while back on DS9 Bajor in going through the last stages of joining the Federation. Kira is still dealing with her "excommunication" from her faith, a lot of political maneuvering, and the usual problems of commanding an important space station.
Since the end of DS9, the novels have continued the story, each book advancing the story of DS9 and her inhabitants. This makes them the most compelling of the Star Trek books and this series is especially nice.