Three girls were best friends - until friendship became murder...

Baltimore police receive an urgent call out to a school after gunshots are heard coming from a locked girls' toilet. The police find three victims, but only Josie is conscious, and she insists she is not the shooter. Perri is unconscious from a bullet wound that has ripped through her jaw; and Kat is dead, shot in the chest.

Detective Lenhardt soon uncovers information that is at odds with the story Josie is telling. Other clues at the scene suggest there was a fourth girl who witnessed the entire episode from behind a locked stall. Where is she now? How did she get out?

The crime seems to reach back five years before this fatal shooting, when three girls met aged ten, and took a vow of eternal friendship. How did that passionate friendship change, evolve - and finally fall apart?