Jessica Barrett, a young English mother living in San Francisco, reveals to her husband, Robert Barrett, that she is pregnant. The couple already has two young children: Ken Barrett and Gail Barrett. The news should be joyous, but a quiet tension lingers as the family navigates a life in the city and the pressures of fame and parenting.
Several days later, during Ken's birthday party, Robert Barrett finds Jessica violently ill and vomiting in the bathroom. After visiting Dr. George Staton, her obstetrician and close confidant, Jessica learns that she is actually three months pregnant, not the mere weeks she believed. The revelation arrives with a chill: the pregnancy has accelerated far beyond what anyone anticipated, casting a pall over the celebration and over Jessica's health.
Over the course of her pregnancy, Jessica experiences extreme mood swings, alarming voices that seem to echo from nowhere, and poltergeist-like phenomena that unsettles the entire household. On one unsettling night, she is awakened by disembodied wheezing and even levitates, wheezing through the rooms of the house. George confides in a worried Robert that Jessica’s pregnancy is progressing at an unbelievably rapid rate, and he grows concerned for her safety. To whom can they turn for help? In a bid to protect her, George arranges for Jessica to spend time with his wife, Barbara Staton, hoping that confiding in Barbara will steady her.
Jessica vocalizes a desire to terminate the pregnancy, but she vacillates, alternating between fear and anger. She even accuses George of murder when he suggests that abortions might be considered if the pregnancy threatens her health. The Barrett household becomes a hotbed of supernatural activity that terrorizes Gail and Ken whenever Robert is away, and Jessica’s behavior grows increasingly disturbing, resembling a possession: her head seems to twist unnaturally, she wheezes with a otherworldly force, and she erupts in violent episodes.
Robert is contacted by a mysterious man named Dimitri, who instructs him to sequester Jessica in their house and to keep visitors away, assuring that the child will be born safely. Jessica grows progressively ill, displaying a fever and stomach ailments, and is bedridden. Under Dimitri’s instructions, George has Jessica placed in a straitjacket to prevent her from lashing out in a fit of violence. When George visits, Jessica alternately pleads for his help before cursing him in a deep, demonic voice. George conducts a series of tests, including brain scans, but none reveal neurologic abnormalities.
After Robert endures a torrent of violent supernatural behavior from Jessica, it is revealed that Dimitri is a lover from Jessica’s past and a Satanist who has arranged for her to give birth to the Antichrist, in exchange for the demonic entity having saved him from dying in a car accident years prior. In a brutal confrontation between Jessica and Dimitri, the demonic entity turns on him and implies that all of the events have been orchestrated for its own amusement. The entity murders Dimitri before departing Jessica’s body, and she immediately experiences a stillbirth.
Some time later, a healthy Jessica accompanies Robert and their children on a boat ride in the San Francisco Bay. Ken unwraps a gift he had earlier acquired, a red toy car hidden in black paper with a gold ribbon. The toy car is revealed as the same model Dimitri crashed in the accident that nearly claimed his life. Ken drops the car over the edge of the boat railing, and his eyes glow green, a chilling hint that he may be the actual Antichrist. The journey ends on a note of eerie ambiguity, leaving the truth of the child’s power open to interpretation as the waves carry them forward.
