Identity
Identity is a major theme in the novel. Mark's Capgras syndrome makes him question the identity of the people closest to him. He believes that his own sister is actually an imposter sent to do him harm. His illness distorts the fabric of his reality, as he feels unable to trust that people are who they say they are. At the same time, Dr Weber struggles with his own sense of identity, as his career as a psychologist is floundering and he has been unable to pursue meaningful new research. Both men, in different ways, grapple with the loss of stability in their life, as Mark cannot trust the identity of others and Weber no longer believes in the professional identity he has made for himself.
Love
Love is another important theme in the book. Karin loves Mark dearly and was the person who primarily raised him. She rushes back to Kearney when she learns he was in an accident and quits her job to care for him. She is crushed when he accuses her of being an imposter, but remains undeterred in trying to help him. Powers underscores the love that Karin feels for Mark by showing how dedicated she is to Mark and how she still views him as her little brother, even into adulthood. More than many of the book's romantic relationships, almost all of which end in disaster or failure, Karin's bond with Mark exemplifies the powerful role that love plays in the book.
Origin
Origin is another key theme in the novel. Karin is hesitant to return to Kearney because it holds too much of the past for her. From her troubled upbringing to her various romantic relationships, Karin feels that Kearney simply has too much of a link to bad memories to ever be a place to which she really wants to return. As a young adult, she left as quickly as she could in order to put that past behind her. Returning dredges up a great deal of emotion for her, most of it unpleasant. In contrast, Mark's life has remained largely the same over the years, as he kept his same friends, job, and car and enjoys many of the same activities he did in high school. HIs life, as portrayed in the novel, exists at a kind of standstill. Powers reveals that places of origin are difficult for his characters, as Kearney seems to trap both Karin and Mark in variable ways.
Environmentalism
Environmentalism is also a major theme in the book. Daniel works to stop the local Sandhill crane habitat from being leveled by a development company that wants to build on top of it. Daniel believes passionately that the cranes should remain undisturbed in their seasonal migration. His quest is seemingly set against impossible odds, but he is steadfast in his devotion to the cause. Towards the end of the book, Mark jokes that Daniel left Kearney because he was tired of being around other people and their flaws. Daniel's quest to save the environment is also indicative of his belief that animals and nature are noble and worth protecting, while humans are, by and large, selfish and cruel.
Religion
Religion is another significant theme in the novel. Karin and Mark grow up in an extremely religious household where their mother insistently pressed Christianity on them. This gave them an ambivalent relationship to faith. However, the note left after Mark's accident suggests that he was actually saved by a divine force. What later becomes apparent was that he wrote that note himself, as he saved Barbara's life and believed that he had been selected to do so. The religious thread of the book runs parallel to the scientific examination of Mark's condition. Mark ends up accepting that while his Capgras syndrome has a neurological cause, his presence on the road that night is somewhat beyond explanation, and is, in his view, the work of a higher power.
Care
Care is also a significant theme in the novel. A few characters are able to show care to people and things around them. Karin returns home to make sure Mark heals from his accident. Barbara, out of a sense of obligation, cares for Mark while he is in rehabilitation. Finally, Daniel works to protect the Sandhill cranes, laboring to prevent the destruction of their natural habitat. Closely intertwined with love, Powers portrays care as a long process with no clear end and many potential hazards along the way. Mark's recovery is filled with setbacks. Daniel's case against the development company is unlikely to succeed. In neither case are the characters overwhelmed by this prospect. Characters like Weber and Karsh are mainly driven by self-interest and are unable to sustain these acts of compassion.
The Mind
The mind is also a major theme in the book. Mark's Capgras syndrome demonstrates the complexity of the human mind, as he is afflicted with an illness that does selective harm to his brain. It makes him view the individuals he is closest to, like Karin, as imposters while leaving his view of others completely unaffected. Likewise, he can remember the night of the incident in flashes but has no complete recollection of events. Powers highlights how, for all of the innovations in neuroscience and psychology, the human mind continues to mystify people. Even the resolution of Mark's illness provides no obvious clues about how to cure Capgras.
