Pretty Poison (1968)

Dennis Pitt, now in young adulthood, has been conditionally released from the psychiatric hospital where he had been institutionalized for an incident that occurred when he was 15. Despite the doctors believing that he is rehabilitated because he no longer suffers from the fantasies that dominated his life, Dennis is still required to check in with his case officer, Morton Azenauer, once a week.

Azenauer will do whatever he can to help Dennis survive in the outside world. A year after his release, Dennis violates the conditions of his release by moving without telling Azenauer, thus missing his weekly check-ins. He moves to Winslow, Massachusetts, where he has gotten a job at Sausenfeld Chemical Co. His boss Bud Munsch, the company, and his acquaintances in town are unaware of his history. In not being truly rehabilitated, Dennis believes the company is part of an alien conspiracy to poison the water supply, including openly discharging chemical waste into the lake next to the plant. Dennis spends much of his time gathering photographic evidence to support his belief. He also becomes infatuated with 17-year-old high-school student Sue Ann Stepanek at first sight. In his "investigative" work, Dennis is able to convince Sue Ann that he is a secret agent and co-opts the eager, admiring girl into his investigations as they begin a romantic relationship. But as Sue Ann deals with what she considers her repressed life, she, in her own slightly off-kilter mental state and using her relationship with Dennis, works toward her own agenda, leading to tragic consequences.