The story is set before and during the Posleen invasion of Earth, but deals specifically with events in Panama. Realizing that the Panama Canal is strategically important, the US sends military and material aid to bolster the defenses, including three warships. Through a complex series of events, one of the ships, the USS Des Moines, gains sentience. The story follows the defense of Panama, both from the perspective of the Posleen-Human conflict, and from the perspective of the struggle between corrupt officials and honorable ones. The Darhel, overlords of the Galactic Federation, want the humans to win, but only just, so that human civilization is shattered and cannot be a threat to them.
The Panama aspects are very interesting, and it shows that both authors have been posted there during their military careers. The story itself is quite good, with predictably excellent battle scenes. It is a worthy addition to the Posleen series, but should probably not be read as a standalone.