La Llave de la Sabiduria = Key of Knowledge (Trilogia de las Llaves)

Following Key of Light, this second installment continues the story of three female friends chosen to free the souls of ancient demigoddesses called the Daughters of Glass. To Dana Steele, books and the knowledge they hold are the key to contentment. But now that search for knowledge must include the second key needed to release three souls held captive by an evil god. She won't be alone, for she's formed fast friendships with two very different women. She can't allow herself to be distracted by the return of the man who broke her heart so long ago, for a danger beyond anyone's imagination is determined to keep her from completing her quest.