Ann Blake is a lonely, divorced, childless English teacher whose ninth grade class includes Karen, a girl who is dying of cancer ( probably lymphoma). As an adjunct to the medical treatment and prayer/faith healing that the child receives, Ann hopes that she might instill in Karen a purpose to live for, through her creative writing
The Infinite Dark refers to a story the students read during that school year, and the teacher ponders on what this phrase really means. She has assumed it means death, but, as Karen regains her health and moves on to another grade and forgets about Ann Blake, Ann realizes that for herself the infinite dark means being unconnected from others, being alone, not making an impact that is permanent--a sort of death in life. As the teacher tries to facilitate healing in the student she ironically realizes that she herself has known little about living her own life.
