The Cult by K.M. Scott

All you’ve ever wanted is yours for the taking. All you have to do is believe.

When Lara Simpson’s sister goes missing, the only clue to her whereabouts is a pamphlet in Rina’s apartment about a new self-help group in town, The Golden Light. Convinced they will lead her to Rina, Lara poses as a new member seeking guidance.
The charismatic leader of the group, a man named Micah who promises enlightenment, seems to care about his followers. However, Lara suspects that the real purpose of The Golden Light isn’t helping people at all, but something far more insidious.
The more Lara learns, the more she doubts that Rina left of her own accord. As Lara descends deeper into the group’s hidden world, she begins to question her own sanity—and wonders if she’ll make it out alive.

Because once you join The Golden Light, you’re a member forever.