Paranormal investigators Ed and Lorraine Warren take on one last terrifying case involving mysterious entities they must confront.

When twin brothers Bill and Hal find their father's old monkey toy in the attic, a series of gruesome deaths start. The siblings decide to throw the toy away and move on with their lives, growing apart over the years.

Arthur must enlist the help of his half-brother Orm in order to protect Atlantis against Black Manta, who has unleashed a devastating weapon in his obsessive quest to avenge his father's death.