Stefano Carloni 
Codename: Fairy. The Fairy Trilogy – Volume II [PDF ebook] 

A year after helping Glitter save Dean Forest from deforestation, the Oak Fairy (Oaky to her friends) has seamlessly integrated into human society, and she works as a 'counter-spy’ with MI6 agent Danny Josephson, with whom she is secretly in love. But in the world of espionage, Death is always lurking; and when a tragic event changes her life forever, the little fairy, to assure justice and save the world, will have to accept the help of a mysterious organisation … a secret society that has its roots in the dark Middle Ages.