It is late June in Ballylack. Hannah Adger anticipates eight long weeks' reprieve from school, but when her classmate Ross succumbs to a violent and mysterious illness, it marks the beginning of a summer like no other. As others fall ill, questions about what - or who - is responsible pitch the village into conflict and fearful disarray. Hannah is haunted by guilt as she remains healthy while her friends are struck down. Isolated and afraid, she prays for help. Elsewhere in the village, tempers simmer, panic escalates and long-buried secrets threaten to emerge.