BABYLONNE, by Catherine Jinks (Candlewick 2008)(12+) is either book 5 of the Pagan Chronicles or book 1 of the Babylonne Chronicles.
At the time of the Albigensian Crusade, Babylonne, the daughter of Templar knight Pagan Kidrouk, runs away from her abusive grandmother and aunt, on a Crusade of her own: to fight the Catholic Church and the French king, who are trying to destroy Toulouse and put down the Cathar heresy.
On the way, she disguises herself as a boy, finds herself in the company of a Catholic priest who apparently knew her parents, and ends up in the middle of a siege...
With terrific voice and great period texture, BABYLONNE is an intense and exciting adventure and provides a fascinating glimpse into the world of the early thirteenth century. Readers will be eager for more.