In northern Iraq, a premonition shakes an elderly priest named Father Lankester Merrin while he sits in a teahouse. He has just taken part in the excavating an ancient Assyrian tomb during an archeological expedition. Merrin pays and leaves, driving his jeep toward Mosul. As the curator of the Mosul museum inventories the artifacts from the tomb, he notices that Merrin has reacted badly to an amulet of the demon Pazuzu. The curator warns Merrin not to return to the United States. Merrin departs anyway, but stops in the ruins of the ancient city of Nineveh, searching for a statue of Pazuzu. He stands before it, his worst fears confirmed. Merrin resumes his journey home, “his heart encased in the icy conviction that soon he would face an ancient enemy” (11).

In the Georgetown neighborhood of Washington D.C., an actress named Chris MacNeil rents a house with her 11-year-old daughter Regan. Their middle-aged Swiss housekeepers, a married couple named Willie and Karl, sleep in a room in the house. One evening, just after midnight, Chris hears tapping sounds while reading her script. She investigates and, as she approaches Regan’s bedroom, the sounds become louder and faster but stop when she enters her daughter’s room.