The program / Gregg Hurwitz.

Enhanced descriptions from Syndetics:

The series that started it all!

In this powerful follow-up to his action-packed thriller The Kill Clause, Gregg Hurwitz, the new maestro of pulse-pounding suspense, ratchets up the excitement with another sensational page-turner featuring Tim Rackley, a driven lawman motivated by honor, morality, and a deep sense of justice.

Called back into the fold of the U.S. Marshals Service, Tim is tasked with retrieving Leah Henning, the daughter of a powerful Hollywood producer, from a mind-control cult. As Tim wends his way deep undercover into an insidious operation called The Program, he confronts a brand of mind-warping manipulation beyond his worst expectations.

Tim becomes enmeshed with a diverse band of characters--from the charismatic, messianic leader T. D. Betters to a cult reject burnout to the intelligent yet highly vulnerable Leah herself--and finds himself caught in a shadowy landscape of lies, manipulation, and terror. At stake: innocent minds--maybe even his own.