"Slaves" (S1 E22) was based on the "girl in the box" sex-slave case, in which Cameron Hooker and his wife, Janice Hooker, abducted Colleen Stan (a.k.a. Carol Smith), then kept her captive and tortured her for seven years.
This is the last episode in which Robert Palm serves as Executive Producer/Show Runner. Palm, who was show runner for only the first season, left the series as he felt too disturbed by the show's dark subject matter. He was replaced by Neal Baer starting in the following season.