In Memphis, TN, Lt. Caroline Mason revisits the 2007 homicide of a 19-year-old man shot to death during a street fight that got out of hand. But when 26-year-old DeMario Thomas went to trial in 2009, the victim’s mother surprised everyone. While in Louisville, KY, a prosecutor’s case comes close to collapse when an unforeseen twist of fate threatens to let an alleged murderer walk.