When an accidental fire is found to have been caused by a bomb, Lilly and the team re-open the 1981 case involving the murder of a yuppie couple.

As the case takes shape, Lilly discovers that the yuppie couple, Jack and Johanna, was hosting a college reunion for their tight-knit group of friends the weekend they were killed. As Lilly digs deeper, she uncovers the friends' ties to a '70s radical activist group and a secret from their past that drove the circle of friends apart, a secret so devastating it led to the murder of two of their own.