A Gathering of Evil is the story of a decent, successful young psychiatrist, Dr. Eugene Martel, caught in a web of lust and perversion which ultimately leads to his destruction.

It is also the story of Rhea, a beautiful woman who lives only to satisfy her never ending sensual desires and to retain, at all costs, her irresistible allure over Dr. Martel, with whom she carried on a torrid affair prior to his engagement.

It is the old story of "A woman scorned". Not only does Rhea seduce Dr. Martel, but she successfully schemes to break his engagement and destroy his career. Her method is a simple one. She engages the aid of another woman who visits the doctor's office presumably as a patient and, while there she forces her attention on him by disrobing and allowing herself to be found nude in the doctor's arms by his fiancee and the clinic's superintendent. He loses his fiancee and is forced to resign from the clinic's staff.

After having discovered that his downfall was caused by none other than Rhea, Dr. Martel resolved to avenge himself and, after having taped the tragic story of his life, and by now completely deranged, he murders Rhea and commits suicide.