Dave Garver is a smooth-talking radio DJ in the small coastal town of Carmel, California, where his nightly show has garnered a dedicated following. During his evenings, he frequently entertains the request of a mysterious female caller who asks him to play "Misty" for her. One night at his favorite bar, Garver encounters a woman named Evelyn Draper. The two share a seemingly innocuous one-night stand without realizing the full implications of their liaison. Evelyn, the woman behind the voice requesting the song "Misty," begins to appear repeatedly in Dave's life. Initially, her presence is flattering, as she seems to be a passionate and attentive lover, focused on making a deeper connection.

However, Evelyn's behavior quickly shifts from infatuated to obsessive. She continuously invades Dave's personal space, showing up uninvited at his home and his work, calling incessantly, and demonstrating a growing possessiveness. As Dave tries to maintain his casual lifestyle, which includes reconnecting with a former romance, Evelyn's actions grow unsettlingly intense. Her adoration turns dangerous, with her feelings of rejection manifesting in menacing ways that threaten to unravel Dave's once-composed existence as she refuses to accept the transient nature of their initial encounter. Dave is drawn into a terrifying situation that challenges his understanding of love and the potentially dark consequences of carelessness in casual relationships.