The Fount of Magic - Songbird River Chronicles, #3

Three heroes, three conflicts.                                       The fate of Songbird River City hangs in the balance. Katherina, the Greatest Fencer in the Realm, faces false charges of murdering Klessia's Master Magician. Serille, the amateur Magician, struggles for a chance to retaliate against those who attacked the Guild of her heart. And Singer, beloved leader of Songbird River City, returns to her homeland after defeating a rogue dragon to find her city in smoldering ruins.
Her greatest fear has come true: her sword, the energy source for her city, has fallen into the hands of the evil Sorcerers in Chirlinia, and with it, the ability to control her enormous robotic Search-and-Rescue machines. And as the three friends journey to different corners of the Two Continents, the Sorcerers' attempts the sow dissonance between them may yet work.