How does the author use duality in the novel, Thendara House?

Bradley's themes of dual identity and dual loyalties are mirrored in the setting of the novel, the travel between the two worlds of Terra and Darkover, and within them the creation of a third way of living, the Guild House. The dichotomies and interrelationships between these, and later with the dynasty of the Forbidden Tower, create the texture of the novel and provide opportunity for many colorful occurrences. Even the narrative is parallel, with events framed by daring mountain rescues at the beginning and end that mark key events in the lives of the main characters. The corporate board rooms of Terra and the feudal halls of Darkover, which contrast yet correlate with each other, are both set alongside the busy commune of the Amazons.