"If I had the ability to stop one of the most insidious plots since 9/11, would I? Would I risk everything, even my own life and the safety of my family members?"

Teenagers Samantha Marie Li Vinte and her best friend Danny Zimmer live in Castle Hedge, a typical small town in southern Ohio where not much of anything ever happens. But their lives are about to be forever changed when Sam inadvertently discovers that a terrorist organization has installed a sleeper cell operative disguised as a substitute teacher at their school.

Mr. Sainclair, who teaches computer design, murdered Sam's...