The Dendarii reach Earth for supplies, medical aide and monetary compensation, and while Miles tries to sort all this out, he gets to know Duv Galeni, essentially his superior in Barrayar's Embassy on Earth, a Komarran who lost his family during the Komarran occupation and now serves as some kind of poster boy for the integration of Komarrans into the Imperial service. And Miles has to juggle his various identities, coming up on the spot with a clone theory when his cover as Admiral Naismith is threatened to be blown. Little does he know at that moment that there's more truth to his invention than he's dreamed possible.
"Brothers in Arms" introduces two major players within the saga: There's Duv Galeni who's going to become one of Miles's closest allies within the service (of course, while grumbling about it), and then there's Miles's clone brother Mark, created by Galeni's father to replace Miles, take over the Empire and usher in a revolution from within against the Vorkosigans and from without in the form of another Cetagandan invasion... at least that's the plan.
Duv Galeni's quite a complex character. As Komarran he's always under suspicion, yet he was admitted into the Imperial Service thanks to Aral. As a history scholar he knows to question what he's been told about the Barrayaran annexion of Komarr, and he knows that sometimes you have to leave the past behind to embrace the future. His confrontation with his father, whom he thought dead, puts all that he's worked for in danger. I absolutely appreciate Galeni, he's complex, he's honest and honorable, and he thinks before acting (something Miles has troubles with at times). And I love the fact that Aral's hunches about people pay off here again, a skill Miles has inherited from his father, to gather people around himself who are not afraid to speak their mind, who are loyal and worthy of Miles (and Aral)'s high regard and loyalty in return.
Speaking of Miles: He's got to convince his adolescent clone who's come to hate him - who wouldn't after having had to endure countless surgeries to physically resemble Miles, endless conditioning to resemble him in his manners and be able to pass off for him (even fooling Ivan who arguably knows Miles best) -, who's come to hate everything Barrayaran that actually there might be a real place for him within Miles's family, within the Barrayaran Empire. The confrontations between those two were definitely the highlight of this novel - and again show off Miles's people skills, his awareness of his unique origin, his loneliness as an only child (and the reasons for that)... and Mark's own yearning for a family and home even though he's not yet ready to act on that and face Barrayar as his own man, not a puppet of a fanatic.
On a sidenote, especially in the light of "Gentleman Jole and the Red Queen", I paid particular attention to Miles saying that, although Aral and Cordelia could have had more children due to advances in medical science especially on Beta, they didn't even consider going down that route due to Miles's ambiguous standing in Barrayaran society.
Things are about to come to a head soon: Is Miles ready to face life on Barrayar? Or are the strings attaching him to the Dendarii, his position at the head of command, not being weighed down by his physical impediments and common prejudice, and Elli who's not willing to settle down on backward Barrayar, too strong? Are Admiral Naismith's days counted anyway now that the Cetagandan might have discovered Miles undercover role? And Mark? Where's he going to pop up next? Great setup for the next stage in the Vorkosigan-saga.