In 1969, Leslie Van Houten and Patricia Krenwinkel carried out horrific acts of butchery on the orders of cult leader Charles Manson. At their murder trial, the lead prosecutor described them as 'human monsters.' But to anyone who knew them growing up, they were bright, promising girls, seemingly incapable of such an crime. Award-winning journalist Nikki Meredith began visiting them in prison to discover how they had changed during their incarceration. The more Meredith got to know them, the more she was lured into a deeper dilemma: What compels 'normal' people to do unspeakable things?