In 1988, in California, cinematographer Dennis moves to the house of his girlfriend Julie to raise a family with her daughters Katie and Kristi. Little Kristi has an imaginary friend named Toby while weird things happen in the house. Dennis decides to place cameras in the house to capture images during the night and soon he finds that there is an entity in the house. Dennis's friend Randy Rosen () researches the events and learns that his house might be a coven of witches and the children may be in danger.
While the jolts and thrills are undeniably subject to the diminishing returns that plague most horror sequels, Paranormal Activity 3 is a surprisingly spine-tingling treat.