Seeking isolation, former psychoanalyst Dr. Verónica de la Serna (Arcelia Ramírez) lives in a remote, fog-shrouded cabin in the Mexican mountains. Her seclusion is interrupted when Marina (Olga Segura), a young and deeply disturbed woman, arrives demanding that Verónica take her on as her final patient. As Verónica initiates psychiatric sessions, a tense psychological cat-and-mouse game unfolds. Unresolved secrets, buried traumas, and deceptive identities emerge, culminating in a shocking revelation that reframes the entire dynamic between doctor and patient.