The film takes place before the events of the first Insidious movie and revolves around Diane Rawlinson (Kate McKinnon), a college student who lost her mother at a young age. Diane is determined to contact her deceased mother through a séance, but things take a dark turn when she inadvertently invites a malevolent spirit into her world. Josh (Patrick Wilson) and Elise (Rose Byrne), experienced paranormal investigators, team up to help Diane and uncover the truth behind the sinister forces that are haunting her.