In the twisty Netflix psychological drama The Sinner (season 2) a great deal of the plot revolves around Marin, a troubled teen who joins a cult but later disappears years before the action we see.
At one point it is suspected she is dead and the police, acting on a tipoff, search a lake and find a body in a car. We assume at the time that the body is Marin.
It later turns out that it is not Marin as she is still alive.
Who is it and what is their relationship to the cult?