Based on the short story "Gramma" and inspired by the works of H.P. Lovecraft, King wrote the tale for his 1985 short story anthology "Skeleton Crew." The Haunting in Connecticut's Peter Cornwell will direct with Matt Greenberg providing the screenplay.
Previously adapted for the small screen as an episode of "The New Twilight Zone" (written by Harlan Ellison), Mercy follows two young boys on a visit to the hospital where they learn that their dying grandmother is a witch and that her powers are fueled by a pact with the Ancient Ones.
Frances O'Connor is also attached to star.
Jason Blum, best known for the Paranormal Activity franchise, will produce alongside McG and Mary Viola.