What could be worse than a school shooting?
When the unimaginable happens and armed men burst into a classroom to take the students and teacher hostage, no one can predict how it will end.
The reason for the attack is unclear but it seems nearly all the hostages are hiding secrets that could have led the gunmen to the school.
After calling the police and evacuating the school, headteacher Cam Cleaver and his deputy, Penny Bainbridge, both realise their own children are among those being held hostage.
When one of the students is injured, both teachers struggle to maintain focus as the lives of their son and daughter are at risk.
But who is really behind the invasion?
And will anybody get out alive?