the vanguard, keith raniere. then came the night sarah says she and four other women submitted, one by one, to being branded. >> and the woman on the table screamed out in pain, twisted and turned and yelled, and the woman i was with holding her legs down, we looked at each other, and we just wept. >> reporter: why didn't you let go, and run out of there, even naked? >> it didn't seem like a choice at the time. >> reporter: authorities allege allison mack oversaw similar branding ceremonies, in which she told women to "feel the pain," and "think of their master" during the agonizing procedure. why would anyone submit to this? sarah edmondson points to years of nxivm training. >> all the indoctrination, all the years of, "women are weak. women have no character. now is the time to prove i can do it." >> reporter: sarah gives another explanation for her obedience -- before she joined the secret sorority and got branded, she says lauren salzman had demanded highly compromising "collateral." >> you need to provide so

sex cult called nxivm, recruiting women and helped turn them into sex slaves for the founder, keith ranierested and mack's co-deficit. in the website -- co-defendant. in the website he posted "there is no merit to the allegations." ♪ one of the alleged victims in this cult is the daughter of actress catherine oxenberg best known for "dynasty." a friend of the oxenberg family spoke about the ordeal they've been going through. >> and she's deeply upset. her family's torn apart. she loves her daughter. she wants her daughter to come home. >> reporter: the cult is based in upstate new york, but authorities say it also has a presence in brooklyn. prosecutors allege nxivm operates under the guise of a secret self-help organization that empowers women. instead, they were turned into sex slaves for ranier, and his initials were branded on to their bodies. choice words for mack -- >> i want to see her put away. she's dangerous. she's sick, she's evil. she's dark and she's done harm to many people. imagine having your initials burned into a woman's body. that's happened. >> we'll continue to follow

. >> reporter: keith raniere, the leader of nxivm, is facing charges including sex trafficking and forcedto that secret sorority. raniere and mack seen together in this video. >> one would say authenticity is being as you are and expressing as you are. >> i don't know why. that makes me want to cry. it's beautiful. >> reporter: former member sarah edmondson say women were forced to sign confidentiality agreements and branded with the symbol incorporating raniere's initials without any anesthesia. >> it was a horror movie. it was the most inhumane horrific way to treat anybody. >> reporter: abc news obtaining documents showing mack now in talks for plea negotiations. an indictment against both mack and raniere says they knowingly and intentionally conspired to recruit, entice, harbor, patronize and solicit persons. it goes on to say they engaged in such acts knowing that means of force, threats of force, and coercion would be used to cause such persons to engage in one or more commercial sex acts. in a letter posted last fall on nxivm's website, raniere said there is no merit to the els th