Karou is a seventeen year old art student in Prague.  Well, among other things.  She's been raised by a non-human bearing the ominous name Brimstone and runs errands to do rather grizzly things for him.  With her blue hair, Karou stands out, anyway, but by her skills and background, she is even more unusual than appearances would dictate.  Taylor develops the story well, beginning with the art student, and gradually expanding our knowledge of her and her skills, `family', and other activities.  Through her life with Brimstone and others in their difficult to access nooks around the world, Karou discovers enemies and peers she wasn't aware of.  In fact a goodly part of the story involves Karou's working to find out who and what she is.  She makes mistakes based on curiosity and impulsivity, but does so mostly through good intentions.  She befriends fellow art student Zuzana, and finds a badly needed loyal tie.  Karou faces many challenges, some from romantic feelings, some from obligation to Brimstone and her surrogate family, some to higher principles, some to humans and non-humans of unsavory lives,  Taylor weaves these all deftly to create a very novel world beyond Karou's Prague home and develops a complex and enjoyable young woman in a well-sequenced way so that the reader unfolds her and her challenges gradually and engagingly.  The created other world and its animosities are also believable in their sentiments, if a bit farfetched as appropriate in a fantasy story, and frightening for Karou.  Too much happens to comment further on events of the story.  That said, while I usually don't consider fantasy my genre of choice, in YA books there seems to be a difference for me.  I thought this worth reading and recommending, and have already purchased its sequel. 

Question: How is the world?
Answer: The created other world and its animosities are also believable in their sentiments