Last of a seven-book series, this is space opera on a grand scale. Galactic empires clash, and elemental beings wipe out entire star systems.
The Klikiss are an insectoid, hive-mind race who were thought to have been extinct for the past several thousand years. Well, they're not extinct, and they want their old colony planets back. The Klikiss are the sort of beings who don't take No for an answer. They are also in the middle of a major "civil war" to see which hive, or breedex, will dominate. With a death toll in the tens of thousands, new genetic material is needed to replenish the ranks, like from slaughtered human colonists on one planet.
Basil Wenceslas is Chairman of the Terran Hanseatic League (Emperor of Earth). He is increasingly isolated and psychotic. King Peter and Queen Estarra are able to flee Earth for the planet Theroc, where they set up a rival Confederation. Many human colony planets switch their allegiance to the Confederation, so Wenceslas sends the Earth Defense Forces to make an example of several colonies. The Ildiran Empire (another humanoid race) establishes an alliance with the Confederation, reducing the number of the Chairman's allies to near zero. The Chairman kidnaps the Ildiran Mage-Imperator, the Ildiran leader, and takes him to an EDF base on Earth's moon until he reconsiders the alliance. Ildirans have a sort of telepathic connection between all members of the race. If any Ildiran is cut off from that connection for any length of time, permanent insanity is a major concern.
Chairman Wenceslas comes up with the idea for an alliance with the Klikiss. He sends one of his senior Generals to negotiate a treaty. The General does not go out of loyalty; he goes because the Chairman does not think twice about holding hostage family members of his senior officers. The general discovers, to his horror, that the Klikiss have no interest in an alliance with anyone. Later, a Klikiss battle group shows up in Earth orbit, with enough firepower to turn Earth into a burned-out cinder. They want to talk to the Chairman, in person, now. He still thinks that he can get whatever he wants, whenever he wants.
This is what good space opera is all about. There is a helpful summary of the rest of the series, so the reader does not have to read it all to understand this book. But it's a very good idea, because the writing is that good. Separately or together, this is very much recommended.