This is probably the best book in the whole series, though Barryar and The Vor Games are so good in their much much different way. The great thing about the Vorkosigan series is that Lois McMaster Bujold has a lot of progenitors in her writing. She loves old military fiction, old science fiction, dystopian and liberation novels, mysteries, fantasy, and here, melodramatic romances.
So this novel is an homage (perfectly executed) to the kinds of society novels that Georgette Heyer wrote. Bujold has a lot of similarities to someone like Connie Willis, who also loves all things British and aristocraty too, but Bujold manages to do it without making me cringe.
So the novel here stays on Barryar, in the capital Vorbarr Sultana, as they prepare for the upcoming wedding between the emperor Gregor and his to be wife Laisa, of Komarr — a love match with an important diplomatic distinction.
So the novel then flits around to a few different perspectives (all still in the particular third person narration the whole series has had, but with an omniscient air): Miles, Ekaterin, Mark Vorkosigan, and Ivan Vorpatril as the different narrative threads circulate. The novel has several interweaving plots — Mark’s ventures with the butter bugs, genetically engineered insects designed to make a fatty/protein substance that has potential, but indistinct possibilities. Ekaterin is trying to get her feet under her, now freshly widowed and a very eligible potential bride. Miles is trying to trick Ekaterin into marrying him (this gets addressed pretty satisfactorily). And Ivan is working directly for his mother, who is planning the wedding, and also tying together the other threads — a Vor house without a direct male heir, a Vor house with the tiniest bit of Cetagandan blood in it, and the bevy of different rivals for Miles.