A plot to assassinate the Vorkosigans with poison gas fails, but the antidote, while effective, is also a powerful teratogen that poses a grave threat to the bone development of their unborn son.

In a desperate attempt to save the fetus, Cordelia has it transferred to a uterine replicator—an artificial womb—to undergo experimental treatment that may partially combat the otherwise-fatal bone damage.

Barrayar, due to its harsh environment, has fostered a deep loathing for mutations, and babies with even minor birth defects are routinely euthanized.

When Count Vidal Vordarian attempts a coup, five-year-old Gregor is rescued by his loyal security chief, Captain Negri, and reunited with the Vorkosigans.

Cordelia, Gregor and bodyguard Konstantin Bothari hide from Vordarian's men in the hills, while Aral and his father organize the resistance.

After the coup, they marry, and in novels set later, are the parents of four young women who combine brains, beauty and, thanks to their mother's training, unarmed combat skills.

[5] The New York Review of Science Fiction (October 1998, number 122) summarizes Barrayar as: open(ing) the later stage of Bujold's oeuvre, most obviously because of its quantum jump in power, complexity and originality, such as the handling of Bothari, and its excursions into women's territory previously untravelled in SF, but also because it initiates a kind of second, deeper pass over the landscape of the earlier books.