Premise: The Paranormal Activity franchise features "found footage" of supposedly real events that occurred to a pair of California sisters who are menaced by a demonic force.
Video camera footage from the fall of 2006 shows a young couple -- Katie and her boyfriend Micah -- settling into their new suburban San Diego home. Katie thinks she's been haunted since childhood by a ghost, and although Micah is skeptical, he sets up cameras around the house to capture any evidence of the supernatural. They leave the cameras rolling while they sleep and record strange sounds and objects moving over several nights. Katie hires a psychic, who suggests the disruptions aren't the work of a ghost but rather a demon. The incidents increase in intensity, including Katie sleepwalking during the night. Just after the couple decides to leave and go to a hotel, Katie, possessed by the entity, kills Micah, tossing him into the bedroom camera. Micah's body is later discovered by the police, but Katie's whereabouts are unknown.
In 2006, Kristi (sister of Katie from the first movie) and her husband Dan return to their Carlsbad, California home one day to find it ransacked. Dan installs security cameras throughout the house, but when their housekeeper Martine tries to help by using sage to cleanse the "evil spirits," he fires her because he doesn't believe in such things. The video cameras catch a series of strange movements and noises that seem to be centered around Hunter. Dan's teenage daughter Ali researches online and finds legends about people making deals with demons that cost them their first-born son, and she discovers that Hunter is the first male child on Kristi and Katie's side of the family for several decades. Kristi recalls being scared by something supernatural as a child but can't remember details; Katie suggests she ignore it because what tormented them as children fed on fear. One night, while Dan and Ali are out, the entity possesses Kristi. Dan calls Martine, who conducts a ceremony and gives him a cross, telling him that it can take away the demon, but the cross -- and the demon -- must then be given to a blood relative. Dan decides to give it to Katie, which triggers the events in the first film. The night after she kills Micah, Katie breaks into her sister's house and kills Dan and Kristi and kidnaps Hunter. Katie and Hunter's whereabouts are unknown.
This prequel begins in 2005 with Katie delivering a box of video tapes to Kristi's house for safekeeping (which are mysteriously stolen a year later during the ransacking from Paranormal Activity 2). Inside are home videos from September 1988 that reveal an ordeal the sisters experienced as girls that they don't fully recollect as adults. One night, mother Julie and stepfather Dennis capture on camera what appears to be a ghostly figure in their bedroom. Intrigued, Dennis sets up cameras around the house hoping to film the entity, whom he discovers is Kristi's "imaginary friend," Toby. He finds what seems to be a demonic symbol written in the girls' closet and sees video of the entity tormenting Katie until Kristi agrees to do what it asks. Kristi requests the family go stay at her grandmother Lois's home, where Dennis awakens one night to find the demonic symbol repeated on the walls behind paintings. He encounters Lois and a group of women dressed in cloaks. He finds Julie dead and tries to escape with the girls, but a possessed Katie screams in a demonic voice that tosses Dennis across the room. An invisible Toby kills Dennis, and the girls walk upstairs with Lois and Toby.
Paranormal Activity 4 (2012)
Five years after the events in Paranormal Activity and Paranormal Activity 2, Katie and Hunter's whereabouts are still unknown. In a suburban neighborhood in Henderson, Nevada, a reclusive single mother (Katie) and her young son move into the house across the street from 15-year-old Alex and her family. When the new neighbor has a medical emergency that requires her to be hospitalized, Alex's parents agree to let the boy, Robbie, stay with them for a while. Robbie introduces Alex's younger brother, Wyatt, to his imaginary friend, Toby, and the two boys share secretive conversations that make Alex suspicious of Robbie's intentions -- especially after Robbie draws a demonic symbol on Wyatt's back. When strange things begin happening around the house -- objects moving, weird noises, shadowy figures -- Alex and her boyfriend Ben set up several laptops to record the goings-on around the house. Katie secretly returns and tells Wyatt that he was adopted and is really her nephew Hunter. She then kills Ben and Alex's mother and kidnaps Wyatt. Alex goes to the neighbors' house, where her father is killed by an unseen entity. She finds Wyatt and tries to get him to run away with her, but she's surrounded by demonic witches and Katie, who attacks.