In rural Somerset in the middle of a blizzard, the unthinkable happens: a school is under siege.

Told from the point of view of the people at the heart of it, from the wounded headmaster in the library, unable to help his trapped pupils and staff, to teenage Hannah in love for the first time, to the parents gathering desperate for news, to the 16 year old Syrian refugee trying to rescue his little brother, to the pregnant police psychologist who must identify the gunmen, to the students taking refuge in the school theatre, all experience the most intense hours of their lives, where evil and terror are met by courage, love and redemption.