Jodi Picoult

Kate has suffered from leukemia since she was a toddler, and her younger sister Anna was conceived for the blood and bone marrow that would help Kate fight the disease. But when it seems Kate might need a kidney, Anna decides that, though she loves her sister, enough is enough.

Seventeen-year-old Peter Houghton wakes up one day, loads his backpack with four guns, walks into the school cafeteria, and kills nine students and one teacher in the span of nineteen minutes. Why?