Sharpened knives and pencil shavings

Tris is starting a new school (surprise, surprise). She meets new friend and reunites and reunites with old friends. She also makes several enemies. To her, everything is fine at first. Then things begin to change: blood in the hallways, knives in lockers, sinister notes.... It soon becomes clear that there is someone that is planning something larger than any pupil could anticipate. With a criminal loose in the school dishuised as friend, foe or even teacher: who can you trust?