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The young actress from California was at a low point during her first winter after moving to New York City when Allison Mack invited her to join Nxivm, a purported self-help group near Albany.

The woman, who was identified only by her first name, Nicole, said she had been trying to build upon an acting career that had included mainly commercial work, and was impressed by Ms. Mack, an actress who had starred in the television series “Smallville.”

Ms. Mack, a senior figure within Nxivm, recruited Nicole as a “slave” in the organization, presenting it initially as an avenue toward fulfillment, then obtaining from Nicole sensitive personal information that was used to control her.

Ms. Mack brought the younger actress to an Albany suburb, perhaps to be near Keith Raniere, the cultlike group’s guru, Nicole testified on Friday at Mr. Raniere’s trial in Federal District Court in Brooklyn.