Spoilers ahead for Count To A Trillion.
Menelaus rouses out of cryogenic slumber to discover that his beloved Rania 's interstellar venture to the antimatter star will not continue with her return to Earth. Instead, she is going onward -- to search out the aliens that will enslave them unless they prove they are capable of maintaining a civilization that can deal with traveling to another galactic cluster and back. (All of which was made clear in Count to A Trillion, which is why reading them in order is probably wise.)
Meanwhile, Menelaus's erstwhile companions, the Hermetists, are trying to remake humanity over into cultures that would survive the alien contact without bothering about the interstellar journey. Blackie gives each of the survivors an era in which to test out his theories. Menelaus tries to interfere when he can, when he wakes from his cryogenic sleep long enough (and ages all the more, to his grief, while Rania remains young in near light-speed travel.)
This book is about their conflicts. It also involves knights in shining (powered) armor and their white horses; an enormous attack on cities that destroys them all (revealed in the first chapter, but with something more revealed in nearly the last); weapons with names, whose owners must not be insulted in their presence; a woman who explains that because she is a dutiful, obedient, meek, and gentle woman, she must not interfere with the matters of war or order about men, so she will leave them to their duty to triumph over those holding them captive and commit suicide for failure; a culture of extravagant luxury where the Nymph Queens cure the ill and erase their memories of suffering; airships that live like sylphs; and much more