The 1970 murder of a musician who was instrumental in creating the Philadelphia soul sound is reinvestigated. The victim tried to keep his involvement in the music scene from his strict minister father. Meanwhile, Lilly meets her teen stepbrother, Finn.

After determining the serial killer's identity - and some of his likely future targets - the team and the FBI work together to apprehend him while trying to locate and protect the people he's preparing to kill.