The Last Session by Julia Bartz

From the instant bestselling author of The Writing Retreat, a white-knuckled locked-room thriller about a social worker who, after coming face-to-face with her dark past, must infiltrate a mysterious wellness center in the deserts of New Mexico.

When a catatonic woman shows up at the psychiatric unit, social worker Thea swears she knows her from somewhere. She’s shocked to discover the patient holds a link to a traumatic time in her past. Upon regaining lucidity, the patient claims she can’t remember the horrific recent events that caused her brain to shut down. Thea’s at a loss—especially when the patient is ripped away from her as suddenly as she appeared.
Determined to find her, Thea follows a trail of clues to a remote center in Southwestern New Mexico, where a charismatic couple holds a controversial monthly retreat to uncover attendees’ romantic and sexual issues. Forced to participate in increasingly intimate exercises, Thea finds herself inching closer not only to her missing patient, but also to tantalizing answers about her harrowing past. However, time is running out, and if she stays for the last session, she too might lose her mind…or worse.