The newest victim of a serial killer is found brutally murdered. Detective Karen Bettancourt, who had been working for eight months with Detectives Tom Selway and Marty Russo on the case, now finds herself re-assigned by the precinct's Lieutenant, Fisk, to partner with Dunbar on the investigation of a stolen car. Just as a resentful Bettancourt begins to think she's being completely marginalized in this new dynamic, Dunbar discovers that the stolen car may be connected with the string of murders.

When Detective Carl Desmond is found murdered, the squad thinks the killer is someone Desmond arrested, but Dunbar believes it's Carl's former police partner.