Undercover Mother

S16 E15: Working undercover to bust a sex trafficking ring, Det. Carisi (Peter Scanavino) stumbles upon Martha Thornhill (guest star Lili Taylor), a mother who has embedded herself as a Madame in the organization for three years in hopes of finding and saving her daughter, Ariel. Martha joins forces with the SVU and they work together to bust the pimp and his cohorts, but Ariel is still missing. Meanwhile, Sgt. Benson (Mariska Hargitay) is confronted with a harsh revelation that will change her life forever.