Long after the Polity has faded into history, the biotech-engineered ruler Yoon has lived for thousands of years and grown numb to ordinary human concerns, until an attack on her world demands restitution. Drawing on technology advanced enough to make nightmares literal, she raises monstrous creatures modeled on Hieronymus Bosch's paintings to hunt down everyone responsible. A standalone novella Asher wrote, by his own account, after a spell of Bosch-inspired nightmares.
Summary by Loreful, from public sources