A tale of the far future. The planet Clio was the subject of an experiment by the centuries ago Psychocrats, seeded with people conditioned to develop the history they wanted, and carefully sealed since its discovery, to protect its inhabitants from the trauma of realizing that. But there appear to be Forerunner artifacts on the planet, so a carefully secret mission goes to attempt to retrieve them.
Roane is dragged along by her uncle, with his son Sandar, because as a family member her uncle can use her with fewer questions. But in the course of scouting about, seeking their object, she is in a building when others arrive, and unable to escape as the men bring in the princess they had kidnapped. An appeal from Princess Ludorica has her helping her escape the kidnappers -- and then helped her escape Uncle Offlas and Sandar, who would have erased her memory and handed her over to her pursuers to hide their mission.
This leads to intrigue, adventure, and action, and includes the question of what, exactly, the Ice Crown of the title and the crowns of other kingdoms do to the people of them; the making of a wreath for an imaginary baby from wayside flowers; hiding behind the kennel of savage dire hounds; an abrupt change in Princess Ludorica as she became queen; a man who claims to have suffered hearing problems ever since another man saved him from a rock fall; and a secret passage into the royal city.