"What the Owl Saw," the second volume in the Buenaventura Series and the sequel to "The Brujo's Way," opens in December 1705 with a terrifying nightmare that fills Don Carlos Buenaventura, a powerful brujo in his sixth life, with dread. Feeling the need to strengthen his brujo powers, always weakened by town life, he rides out into the wild mountain landscapes around Santa Fe in order to practice his sorcerer's technique of transforming himself into hawks and owls. Transformations are exhilarating, but they do not dispel his sense of an impending menace. In addition, as he tells his friend...