Astrid Llewelyn is now a fully trained unicorn hunter, but she can't solve all her problems with just a bow and arrow. Her boyfriend, Giovanni, has decided to leave Rome, the Cloisters is in dire financial straits, her best friend's powers seem to be mysteriously disintegrating, and Astrid can't help but feel that school, home, and her hopes of becoming a scientist are nothing but impossible dreams.
So when she's given the opportunity to leave the Cloisters and put her skills to use as part of a scientific quest to discover the Remedy, Astrid leaps at the chance. Finally, she can have exactly what she wants - or can she?
At Gordian headquarters, deep in the French countryside, Astrid begins to question everything she thought she believed: her love for Giovanni, her loyalty to the Cloisters, and - most of all - her duty as a hunter. Should Astrid be saving the world from killer unicorns, or saving the unicorns from the world?