A man accused of opening fire on a crowd from a multi storey car park, and killed a policeman, is claiming his innocence. Boyd's colleagues question his loyalties when he seems unwilling to re-investigate. As DC Mel Silver digs deeper, she discovers some disturbing truths about her boss.

Boyd struggles with his past while continuing the investigation on a mass murderer who was also guilty of killing his close friend. Are the Gunman's claims of innocence true? As the team investigate it looks as if someone else may have been involved.