The Hour I First Believed - Wally Lamb

When high school teacher Caelum Quirk and his wife, Maureen, a school nurse, move to Littleton, Colorado, they both get jobs at Columbine High School. In April 1999, while Caelum is away, Maureen finds herself in the library at Columbine, cowering in a cabinet and expecting to be killed. Miraculously, she survives, but at a cost: she is unable to recover from the trauma. When Caelum and Maureen flee to an illusion of safety on the Quirk family's Connecticut farm, they discover that the effects of chaos are not easily put right, and further tragedy ensues.