Apparently, the story that Mike Flanagan and co. are crafting for Midnight Mass is all coming from their own imaginations and not a pre-existing work of literature.
Besides, he already has another book adaptation for Netflix in the works called The Midnight Club, inspired by the young adult novel by Christopher Pike.
Quite frankly, I like the idea of Mike Flanagan returning to developing his own material for this new series.
This marks a departure from both The Haunting of Hill House, which was loosely based on the classic 1959 novel of the same name by Shirley Jackson, and The Haunting of Bly Manor, which was one of two adaptations of Henry James’ The Turning of the Screw which Mike Flanagan personally shot down in a tweet from January 2021.