When a woman with no identification is found dead from a blow to the head with a pavement stone, the only clues to her past are found in the information stored on her mass-transit pass. More magnetic evidence leads Detectives Briscoe and Green to the current possessor of the dead woman's credit card; but once they have their suspect, the mental state of the attacker calls into question whether the perpetrator alone is responsible for the tragedy. Following a plea to action from the deceased's husband (Ty Burrell), District Attorney Lewin pursues media glory by encouraging prosecutors McCoy and Carmichael to take on the health care system responsible for releasing the emotionally disturbed convict into society.