Astrid finds out that there are killer unicorns that exist on earth and that she is part of a long line of warriors destined to fight them. Astrid's mother is rather eccentric. She believes in extinct killer unicorns, something which Astrid has grown up hearing about.
The story begins with 16 year old Astrid spending a nice romantic evening under the stars with her boyfriend. Her boyfriend has been pressuring her to "do it" with him. Astrid just hopes that he will ask her out to the prom. Just when he starts making moves on her, a unicorn appears. Astrid is able to approach and pet the unicorn however the unicorn attacks her boyfriend. Astrid gets her Mother to help as her boyfriend will die from the unicorn horn poison. Her mother administers something called the Remedy. Her boyfriend is shipped off to the paramedics believing that he was slipped drugs and attacked by a rabid goat.
Astrid's mom is excited that there's proof that killer man-eating unicorns still exist and begins contacting other believers. Astrid comes from a long line of women who can catch and kill unicorns - but only if they remain virgins. Her mom wants her to join the Cloisters of Ctesias, which is a training ground in Rome for unicorn hunters. Astrid is reluctant as she wants to do normal things and become a doctor. Her mother convinces her that she can fulfill her desires to be a healer by finding out how the secret Remedy works.
Astrid is flown to the Cloisters of Ctesias in Rome. The Cloisters turns out to be a bunch of fairly run-down ruins. The first person she meets is Cory, who turns out to be her roommate. When she shows her their room, there is a baby unicorn on her bed. Cory surprises Astrid by literally launching the unicorn out the halls and over the balustrade. Apparently unicorns are hard to kill as they regenerate. The unicorn is called Bonegrinder and is the house zhi (a breed of domesticated killer unicorn). Apparently the unicorn is around as a kind of virginity test for the hunters. Cory is rather bloodthirsty and prepared to be a huntress while Astrid is doubtful and wondering whether how she treats the unicorn is wrong. But, Cory really worships Astrid's family because her family are the Llewelyns who are famous for the best hunters. She and Cory explore the premises of the Cloisters to find a good place to put Bonegrinder.
Soon, Astrid's popular cousin Phillipa (Phil) arrives at the Cloisters. The girls find out that the re-activation of the Cloisters of Ctesias and the Order of the Lioness unicorn hunting training program is sponsored by a pharmaceutical company. Astrid immediately feels a sort of affinity for the scientists and their motivations to research the Remedy. They find out that there has been an upsurge of unicorn attacks lately - Phil thinks that's why the program to train huntresses was re-started. Phil convinces Astrid to escape the Cloisters for a while and experience Rome. On her outing in Rome, she meets Giovanni. Later on, as Giovanni is escorting her back to the Cloisters, Astrid sees another killer unicorn but the unicorn disappears making Astrid look crazy.
That night when Astrid and Phil sneak back into the Cloisters they are caught by Cory and the don of the Cloisters, Neil. Neil is angry at the girls and tells them that unicorns are drawn to hunters and that them going out among other people can endanger those people. Neil also firmly states that the girls are not allowed to date when they're part of the Order of the Lioness. Phil objects highly to this and Astrid argues why can't they update the rules to fit modern day women's lifestyles. Neil admits that he doesn't really know the right thing to do as he is new to the job as don.
Over the next few days the rest of the girls arrive. Astrid learns that there are many ways to test virgin girls to see if they are fit to become unicorn hunters. Unicorn hunters are very strong and also immune to the unicorn horn's poison. She also learns more about Alexander the Great and how part of his greatness was because his horse, Bucephalus was actually a unicorn that he conversed with. She and the other girls train in weaponry fit to kill unicorns. Apparently unicorns cannot be killed with bullets as Cory, almost cruelly proves, when she shoots Bonegrinder and the baby unicorn gets back up a second later, unhurt. Astrid is pressure more and more to meet the expectations of a Llewelyn. She would much rather follow the scientists around as they study the Remedy.
One day, Phil takes Astrid out of the Cloisters again so that they can meet Giovanni and his friend. They meet the boys and tour an art gallery. Astrid starts to fall in love with Giovanni. She decides that Giovanni is the one she wants to lose her virginity to. In a heated moment, Giovanni finds out Astrid is a virgin and being a gentleman, stops himself from doing anything they'll both regret. She and Giovanni have a bit of an argument but reconcile before Astrid returns to the Cloisters.
One night, the girls are stationed in a farm out in the Italian countryside for their first official hunt. After a long wait, they see a rogue unicorn which they try to take down but only succeed in wounding it before it escapes. They eventually kill it. Astrid finds the whole process really cruel and barbaric and she doesn't want to do it anymore. She tries to phone her mother to tell her about it but her mother doesn't understand why Astrid feels this way and isn't proud to be a Llewelyn huntress.
Phil and Astrid escape the Cloisters again. Giovanni wants Astrid to tell the truth about who she is and why she is in Rome, living in the old ruins of the Cloisters. Astrid finally tells Giovanni the truth. It's only when a pack of unicorns appear in the park where she and Giovanni are making out that Giovanni finally believes her.
Phil and Astrid convince the don of the Cloisters to allow all the unicorn hunters a break to roam Rome for a bit. Before they leave, Astrid receives a sort of mean phone call from Giovanni where he acts as if Astrid has snubbed him. As expected, once the girls are out in the park, a unicorn finds them and tries to attack them, succeeding in injuring several of the girls before Astrid puts an end to it. Phil and Astrid discover that Marten, the head scientist, is eager to get his hands on their kills but doesn't seem to care about getting them proper trainers or helping them out during major emergencies.
One night, after she had gone out to visit her boyfriend, Phil returns to the Cloisters behaving unlike herself. When Bonegrinder tries to attack Phil, Astrid finds out that Phil is no longer a virgin and that she might have been raped. Angered and upset, Astrid goes out in search of Phil's boyfriend but encounters a huge unicorn. Surprisingly, instead of trying to kill her, the unicorn attempts to communicate with Astrid through images. Astrid eventually learns the huge unicorn calls himself Bucephalus. Astrid returns to the Cloisters and comforts Phil. Soon after, Giovanni makes a surprise appearance at the Cloisters and tells Astrid that Phil's ex-boyfriend has gone missing and he needs her and Phil's help. Giovanni reveals that he and Phil's boyfriend had been paid by someone named Alexander to date Astrid and Phil so that they won't join the Order. Of course, this angers Astrid even more but she listens to his story. Eventually she finds out this mysterious man named Alexander is actually Marten, the head scientist that is sponsoring the Order. Upon further investigation, they find out that Marten and his team of scientists are gone.
The don decides to find out the truth of the matter. He leaves the girls in the care of Astrid's Mom, who is well-versed in the history of the Order. When Astrid's mother arrives, Astrid is immediately pressured again to be the best Llewelyn huntress and bring in the most kills and outshine all the others. Her mother turns out to be a slave driver of a trainer that has little to no patience for Astrid having doubts about who she is and what she's supposed to do.
On another hunting run, the girls are ambushed by a pack of unicorns. During the attack, Astrid sees that when she stabs the unicorns, they aren't healing themselves. Astrid herself is stabbed by a unicorn. Somehow Bucephalus, the huge unicorn appears on the scene and heals her. Bucephalus communicates with Astrid that the unicorn killed her as a trophy of vengeance against the huntresses. Astrid also learns that her huntress famous descendant Clothilde, had not really died from Bucephalus killing her but had pretended her death so that she could go on and marry and have children. Bucephalus leaves Astrid, after asking Astrid to end the growing tension between humans and rebel blood thirsty unicorns that is starting up again by the false Alexander - Marten, the scientist.
Eventually Astrid will learn the truth about what Martens is up to and the motivations behind the rebel unicorns and Bucephalus' role.
Best part of story, including ending:
I like the novel idea killer man-eating unicorns and the interesting species of unicorns described in the story.
Best scene in story:
My favorite scene is at the beginning, when Astrid and her boyfriend were supposed to have a romantic night under the stars but the unicorn shows up. I think it's hilarious.
Opinion about the main character:
I like that Astrid is interested in medicine but is pressured by her crazy mother to become a huntress. It makes for an interesting dynamic.