Someone is killing people related to Benson's old cases. As the unit tries to find the killer, Benson struggles with the guilt that people are dying because of a vendetta against her. Eventually, the detectives hone in on a man that Benson sent to jail for seven years, who was recently cleared via DNA evidence. Wrongly sent to prison, the man's bitterness has turned deadly, and he won't stop until he makes Olivia pay for her tragic mistake.