S3, E22: Stella is a murder suspect when her DNA matches the evidence in a Philadelphia cold case. Mac's career is put in jeopardy. Stella is forced to deal with painful memories when Det. Valens (Danny Pino) visits the lab and says her DNA is connected to a Philadelphia cold case making her a suspect, and Mac's career is put in jeopardy when an internal investigation is opened against him. (TV-14)