Pregnant with her third child, the young English mother of two, Jessica Barrett, is living a happy life in San Francisco with her respectable record producer husband, Robert. Puzzled with her strange pregnancy, more and more, Jessica finds herself affected by this unnatural situation, exhibiting erratic and violent behaviour, while talking with a deep, almost demonic voice. Could she be possessed? As blood-curdling incidents threaten the family's peace, an old friend from the past arrives, claiming that he has all the answers. But, who is this new and appalling Jessica?