Astrid Llewelyn is now a fully-trained unicorn hunter, but she’s learning 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 fears 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 the Gordian Pharmaceuticals 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?