A Serbian artist, Irena Dubrovna, has a chance encounter at a New York City zoo with Oliver Reed, a charismatic engineer. Their initial connection swiftly grows into romance, leading to marriage. However, their married life is overshadowed by Irena's deep-seated fear stemming from an old family legend. She believes she is descended from a group of people who turn into panthers when emotionally aroused, especially due to anger or jealousy. This fear prevents her from becoming physically intimate with Oliver, causing strain and confusion in their relationship.

As Irena's paranoia intensifies, Oliver turns to his colleague and confidante, Alice Moore, for support. Suspecting there might be a rational explanation for Irena's fears, Oliver enlists the help of Dr. Louis Judd, a psychiatrist, hoping he can dispel Irena's deep-rooted anxieties. Meanwhile, Alice becomes increasingly important in Oliver's life, a fact that does not go unnoticed by the troubled and increasingly isolated Irena. Haunted by both internal and external forces, Irena’s grip on reality starts to unravel, leading to a series of tense and eerie occurrences that blur the lines between myth and reality.