The narrator, who has been a counselor at a summer camp, brings a friend home to meet her computer-wizard older brother, Eric, but finds him acting very strange--overprotective, defensive, and aggressive. Later his inexplicable behavior shows up at the dinner table. He is unreceptive to parents' inquiries. Readers learn some of the delusional thoughts from italicized passages interspersed with the narrative of a family recognizing mental illness and making treatment decisions.

Eric is hospitalized after an episode in which he threatens the family with a kitchen knife. He is released on medication in a matter of weeks, but continues to behave strangely if not dangerously--he asks his sister at one point if she knows any "secret numbers"--and she realizes his new condition is not simply going to go away, but has opened a whole new chapter in family life and requires new and careful adaptations.