Mark is a twenty-something resident of Kearney who suffers a severe brain injury and cerebral edema following a near-fatal car crash. Before the accident, he works a routine job, spends time playing video games with close friends, and takes immense pride in his Homestar modular house and his dog, Blackie. Upon waking, he exhibits echolalia and develops Capgras syndrome. This rare neurological condition causes him to believe his older sister, Karin, has been replaced by an imposter. Because his emotional processing center is disconnected from his visual recognition, he continually invents detailed conspiracies to explain why his sister, his dog, and his home feel completely alien to him. He fixates on a mysterious note left by his hospital bed, hoping it holds the truth about his altered reality.

Karin is Mark's older sister and lifelong caretaker. She has spent much of her life acting as his protector, shielding him from their parents' erratic religious and paranoid behaviors. She works in customer service and immediately drops her routine to manage Mark's hospital care, taking meticulous notes on his progress. When Mark develops Capgras syndrome and rejects her as an imposter, Karin loses her primary source of personal validation. Without her brother's reliance on her, she finds herself adrift and seeks comfort in past romantic relationships while attempting to establish an identity independent of her caregiving role.

Gerald is a successful neuropsychologist who writes popular science books composed of humanizing case studies of patients with rare brain conditions. After decades in his field, he enters a period of severe professional doubt, triggered by negative reviews accusing him of exploiting his subjects and ignoring modern neuroscience. Seeking a distraction from his dissolving sense of identity, he travels to Nebraska to evaluate Mark's trauma-induced Capgras syndrome. He initially attempts to maintain a clinical distance, utilizing tools like a galvanic skin response device, but finds himself increasingly disoriented and ineffective in his treatment recommendations.

Barbara is a nurse's aide in her forties who works at the local rehabilitation clinic. She projects an aura of absolute calm and self-containment, immediately putting both Mark and Karin at ease. Unlike the medical doctors who frustrate Mark with endless tests, Barbara forces him to do things for himself and offers straightforward interaction. Her composed exterior makes her a stabilizing force in the clinic, drawing the attention of Gerald Weber and serving as a role model for Karin.

Daniel is Mark's estranged childhood friend and a passionate conservationist working for the County Crane Refuge. He monitors the sandhill cranes that migrate along the Platte River, actively fighting against local development plans. Daniel lives a life of extreme self-denial; he is a strict vegan who barely eats and practices daily meditation to detach from his ego, with the goal of flowing like water. His intense dedication to the natural world isolates him from the human community, making his public pleas to save the crane habitat fall flat.

Robert is a practical, business-driven land developer leading a local consortium in Kearney. He plans to build a development project, potentially involving a water park and zoo, that requires diverting water from the Platte River. This move directly threatens the historic sandhill crane habitat. He is an earthy man who embraces his appetites, contrasting sharply with the local conservationists. He argues convincingly at city council meetings that his development will safely manage tourism and benefit both the town and the birds.

Sylvie is Gerald Weber's wife of thirty years. She shares a deep, instinctive bond with him, functioning much like the lifelong mating pairs of the sandhill cranes. She understands Gerald's routines flawlessly and dismisses the negative reviews of his latest book as irrelevant. She seeks to maintain the stable, familiar dynamic of their marriage, actively rebuking Gerald's growing self-doubts because any fundamental shift in his professional identity forces her to reevaluate her own life.