Nocturnal (2018)

Marine biologist Dexter Harris returns home to discover his wife and child have been murdered during a home invasion. When their killers receive lenient sentences, Dexter struggles to cope. He begins therapy with Dr. Miranda Miller, who diagnoses him with post-traumatic stress disorder. As their sessions continue, Dexter's mental state deteriorates, and he starts to mentally replace Dr. Miller with her daughter. Learning about Dr. Miller’s husband, Kevin, fuels his rage and leads him to kidnap and murder his family’s killer, Raymond Tucker, and then Kevin himself. Dr. Miller races to find Kevin before he can be harmed, suspecting Dexter's involvement.