The continuing tale of Boskone and Kimball Kinnison.
In the opening, he recounts to the Admiral and another high official that he does not know if Boskone was annihilated by their attack. The rest is the somewhat episodic adventures of working out that they did. And fighting onward.
Eichlan speaks for Boskone here -- a harsh, pitiless cold-blood race of Eich being those trying to control the galaxy and rip Civilization's position away. Kinnison poses as both a high society man and as an asteroid prospector with a weakness for booze and the drug bentlam, using planets as weapons, deducing what other galaxy has to be a problem*, a discussion of a Kipling poem, the problems that teething causes when you use a regenerative technology, a Dr. Phillips dubbed so in self-defense, so they didn't have to pronounce his real name, and more.
*Because it's the only other one to have a significant number of planets. Old science said they had to be rare, and Smith posited a collision of two galaxies to provide the number he needed.