Pretty young Serbian immigrant Irena Dubrovna is making a sketch of the black panthers kept in captivity at the zoo inside New York’s Central Park. While there, an engineering draughtsman named Oliver Reed is struck by her exotic good looks and proceeds to strike up a conversation with her. The conversation goes better than expected for Oliver and Irene invites him back to her apartment for tea. As they leave, the viewer is given their own treat: quick peek at some of the sketches made and discarded by the artist including one showing the beautiful black feline impaled by a rather fiendish sword.
Lo and behold, when Oliver gets inside Irena’s apartment he is treated to similar image in statuary form: the medieval warrior riding triumphantly on horseback is showing impaling a cat with a sword. Clearly, Irena’s relationship with big cats is troubling to say the least. Oliver soon learns that the warrior is a Serbian king named John and the cat is actually more symbolic than real: the cat represents evil that must be annihilated. The legend of King John impaling evil the cat traces back to a time long ago when Christians in the village she calls began to delve into witchcraft and the black arts in response to bondage at the hands of the Mameluks. King John arrived, drove the Mameluks out but felt compelled to engage in a bit of genocide when he realized that the villagers had all succumbed to devil worship.
As one might naturally suspect…not long after this Oliver and Irena get married!
The marriage remains unconsummated for a very disturbing reason: if she indulges in intercourse with her new husband, the latent evil passed down through generations of her Serbian blood will rise to a boil and erupt in a most fantastic way. Irena will literally transform into ravenous, bloodthirsty feline.
Like any good husband would, Oliver’s reaction to this sexual frustration is not forcible taking of his property, but sending his wife to a psychiatrist, Dr. Lewis Judd. Judge is a rather shady character who quite obvious is drawn to the repressed sexual tiger lying in wait inside Irena and he very nearly convinces her that her problem is entirely mental. The truth is presented as something more ambiguous for much of the film, but in the movie’s most unnerving scene it becomes increasingly clear that some sort of wild animal is trapped inside Irena and it probably is a ferocious catlike creature with enormous claws.
Or, perhaps, it is merely a most incendiary form of jealously. As Irena pushes her husband away, his purely platonic close friendship with Alice Moore starts to move closer and closer toward the romantic. At least it does from Irena’s point of view. This point of view is not helped at all by Alice’s confession of deeper feelings to Oliver. One fateful night, Alice decides to head to a public pool for a swim and in the movie’s most intensely terrifying sequence she can hear the sound of a prowling cat echoing off the tiled floors and walls in the nearly abandoned building. The ambiguity surrounding the truth of Irena’s condition is ultimately revealed when Alice—ready to believe she imagined the whole thing—discovers her clothing ripped to shreds.
After one last meeting with Dr. Judd, Irena feels she is ready to be the wife Oliver has waited for so long only to discover that she herself waited too long. Oliver tells her he has fallen in love with Alice and plans to divorce her. He leaves for work and later in the office Oliver and Alice are together when they realize they are not alone. In fact, they are being cornered by some ravenous, wild animal way too large to be a mere house cat. As the animal is nearing the point of attack, the engineer picks up one of the tools of his trade: a large T-square. As he holds the tool over his head, the shadow it casts on the wall make it look more like a Christian cross and seems to be invested with the power to overcome the ferocity of the beast.
Alice immediately calls Dr. Judd to warn him to keep away from Irena because of the very real danger she presents, but the doctor cradles the phone when she appears in his doorway. His sexual attraction overwhelms his good sense as well as his fear and he pays the ultimately price for his unhinged desire: Irena becomes a black panther and leaves the doctor bloodied and dead. Irena assumes her human shape at the arrival of Oliver and Alice and heads straight for the zoo. When she get there, she enters the panther’s cage using a stolen key and, as might be expected, is herself ripped to shreds by the big black cat. The panther manages to escape
After the animal leaves, Alice calls Judd to warn him to stay away from Irena. But he hangs up when Irena arrives for her appointment with him. Attracted to her, Judd forgets his medical ethics and kisses Irina passionately. She transforms into a panther and kills him. When Oliver and Alice arrive, Irena slips away in her human shape and goes to the zoo. There she opens the panther's cage with a stolen key and a vicious fight ensues. A black panther escapes but is killed by a cop driving by in a car.