This novel is based on the facts of an actual hantavirus outbreak that took place in the southwestern US in 1993, retelling the events as medical mystery, as ghost story, and as meditation on the relationship between rationalist western medicine and the beliefs of local indigenous cultures.

Dr. Push Foster is part Choctaw and part white, raised in Oklahoma. He returns to Arizona as an Indian Health Services physician at the time an outbreak begins of what is later identified as Hantavirus Pulmonary Syndrome. Western medicine and traditional health beliefs and practices overlap in the investigation and response to the illness as it infects and kills Navajo people.

Querry presents us with a convincing epidemiological investigation into the virus, but also suggests an alternative, or complementary, etiology for the outbreak: an archaeologist has stolen a sacred stone from the Hopi people with the help of a Navajo witch, or shape-shifter, the title's "bad medicine" practitioner. This theft, the novel suggests, is the reason that only Navajo, and one white person (the archaeologist's partner) become ill.

The climax of the story is a showdown between the shape-shifter, a Hopi village headman, and the ghost of a woman killed trying to save her people from the 1805 massacre of Navajo by Spanish troops at Muerto Canyon. (The virus, when first identified, was named Muerto Canyon Virus.) This woman becomes a figure of both vengeance and reconciliation, an uneasy meeting of cultures that echoes and informs the work of Push Foster and his colleague, Sonny Brokeshoulder: both are men of Indian blood with a "white" upbringing and who return to their culture bearing Western medical training, but do not deny the traditional knowledge either.

Unlike most medical thrillers, this book does not offer reductive explanations and answers; instead, we are left with the certainty that traditional and western thinkers must collaborate, not only to care for patients, but to take care of the natural environment on which all our health depends.