In a quick prologue, set in 2005, Katie (Katie Featherston) drops off a box of old videotapes to be stored in her sister Kristi's basement. The content on these tapes consists of 1988 footage of young Katie (the main character of Paranormal Activity) and Kristi (the main character of Paranormal Activity 2). As kids, the girls live with their mother Julie (Lauren Bittner) and Julie's loving boyfriend, Dennis (Christopher Nicholas Smith). Kristi starts spending time with a sinister-sounding "imaginary friend," Toby, and strange, terrifying things start happening in the house. Dennis videotapes everything, but is anyone really prepared for the true horror behind it all?
