"You can’t go home again" — in what deeply intriguing and surprising ways that familiar phrase explains “The Echo Maker,” Richard Powers’ ninth novel and winner of this year’s National Book Award for fiction. Thirty-something Karin Schluter is suddenly called back to her hometown of Kearney, Neb., after her younger brother Mark flips his truck in a near-fatal accident. Living now in Sioux City and having recently buried the last of her fanatically religious parents, Karin had begun to wean herself from her past. However, Mark, whom she practically raised, is her only near kin. She has no choice but to return home.

The first indication that home isn't the same comes when Mark awakens from his coma. Although the 27-year-old slaughterhouse mechanic and good old boy recognizes his sister, he doesn't believe it's her. Instead he views her as an imposter. Mark is manifesting signs of Capgras syndrome, a rare neurological disorder whose sufferers believe their loved ones have been swapped with lifelike robots, doubles or aliens. As Mark's doctor explains to Karin: "He knows he has a sister. He remembers everything about her. He knows you look like her and act like her and dress like her. He just doesn't think you are her." Though devastated, Karin gives up her job to remain in Kearney.

Physicians and caregivers assist Mark. Nurse's aide Barbara Gillespie becomes his Florence Nightingale, though there's something peculiar about her. Faintly echoing Mark's condition, everyone who meets Barbara finds her strangely familiar -- they recognize her but can't place where.

That is only one of the novel's mysteries. What, for instance, caused Mark, an expert driver, to flip his truck? Three sets of tire tracks were discovered at the scene of the accident. And who wrote the enigmatic note found on Mark's bed stand the night he was admitted to the hospital? "I am No one but/ Tonight on North Line Road/ GOD led me to you/ so You could Live/ and bring back someone else."

Powers, who typically uses science to explain our lives, has never been a spiritual writer, yet early on one wonders where these mysteries, or red herrings, will lead.

With no cure in sight for her confused brother, Karin in desperation contacts celebrated New York cognitive neurologist, Gerald Weber. Weber is famous for writing case histories of bizarre brain disorders in the vein of Oliver Sacks' "The Man Who Mistook His Wife for a Hat." Serving as Powers' mouthpiece on the intricacies and mysteries of the brain, Weber becomes increasingly close to Karin, Mark and Barbara.

Like the other characters who come in contact with Mark, Weber falls into unfamiliar territory as his once stable marriage begins to shake and his professional reputation is threatened by reviewers who attack his latest book and question his ethics.

Although Mark's neurological disorder remains the novel's focus, Powers devotes attention to Kearney's greatest attraction: the half-million sandhill cranes that return each winter and generate a spectacular sight for the "crane peepers." The cranes, which annually retrace a route laid down centuries before, enable Powers to elaborate on the mysteries of migration, familiarity and extinction affecting all living creatures. Their familiar route along the Platte River, however, is threatened by a development project, a village/theme park for crane watchers, which pits Karin's two former (and perhaps current) boyfriends as adversaries.

In this deeply layered and rich novel about neuroscience, migratory patterns, environmentalism and the improvised human self, Capgras works as a controlling metaphor. Though the syndrome is rare, Powers demonstrates how estrangement and familiarity figure not only in misidentification delusions but also in everyday human and animal behavior. Karin, who feels herself doubled between the real sister and imposter sister, is losing track of who she is. Mark is convinced that his sister, dog, home and entire hometown have been switched, as if his life were a kind of "Invasion of the Body Snatchers." Even Weber, the stable man of science, is behaving in ways unfamiliar to himself and his family.

All this, of course, relates to 9/11, which figures in the novel's background. Mark flips his truck a few months after the attack on the twin towers, and a few days after he and a friend sign up to join the National Guard. By the novel's conclusion, Operation Iraqi Freedom has begun. Powers has written a beautifully subtle and barely visible allegory, in which Capgras and Mark's feelings of estrangement mirror what happened to America in the days following 9/11.

As if all this were not enough to indicate that "we can't go home again," Powers offers that such entities as home and self are more provisional than we may think. Karin, Mark and the others strive to conceive of themselves as possessing a whole and monolithic self, yet the neurological evidence, along with their experiences, indicate that the self is deeply fragmented and discontinuous. As Weber states, "We think of ourselves as a unified sovereign nation. Neurology suggests that we are a blind head of state, barricaded in the presidential suite, listening only to handpicked advisors."

Readers are likely to come away from this novel with a new understanding of how we deceive ourselves and of what happens when the brain breaks down. "My brain," says Mark, "all those split parts, trying to convince each other. Dozens of lost scouts waving crappy flashlights in the woods at night. Where's me?"

Powers, whose stock as a novelist continues to rise, has been praised as a writer of "blistering intellect," yet criticized for sacrificing the emotional credibility of his characters to his ideas. In other words, his ideas tend to overshadow his people. Such criticism, however, feels increasingly less applicable. With "The Echo Maker," one of his finest fictions to date, Powers has fashioned a beautifully unsettling novel, revealing the fragility and uncertainty of the human condition while generating a sense of awe and wonder at the natural world.

(James Schiff is associate professor of English at the University of Cincinnati.)