Every memory Ava Sorelle has of her childhood is set in a house with two rooms-a kitchen, and a bedroom. Raised by a reclusive guardian who insisted they were in witness protection, Ava was never allowed to step outside. One day, when she's thirteen, the guardian disappears. Rescue teams find the house abandoned... but with three rooms, not two. A study filled with journals, photographs, and files on dozens of missing people-including Ava herself, listed as having died at age five.

Fifteen years later, Ava is a trauma therapist specializing in dissociative disorders. But her world unravels when she begins treating a new patient: a man who remembers her from the "third room" and insists they were kept there together.

As Ava investigates, her grip on reality begins to slip. Time fractures. Her patients begin vanishing. And someone is leaving her messages only she can read-written in her childhood handwriting.

What if everything she remembers was planted? What if she isn't Ava at all? And what lies beyond the fourth wall?