Inspired by H.P. Lovecraft, the short story "Gramma" was written by Stephen King for his 1985 short story anthology "Skeleton Crew."
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 playing the mother.
Peter Cornwell will direct the horror thriller, to be released by Universal Pictures. Jason Blum and Wonderland's McG and Mary Viola are producing. Matt Greenberg wrote the script.