The 1963 shooting death of a wandering pool hustler is reinvestigated when the murder weapon is discovered at a pool hall during a renovation. The probe reveals the victim played there just days before he died and that he was gunned down on the same day President Kennedy was assassinated.

The sixth season ends with the investigation of a female cadet's 2005 murder at a local military academy, where she was resented for being the first female cadet. The case dredges up unpleasant memories for Lilly, who recalls her own difficult journey to become the first female homicide detective in Philadelphia.