The Sundial — Shirley Jackson

Aunt Fanny knows when the world will end....

Aunt Fanny has always been somewhat peculiar. No one is surprised that while the Halloran clan gathers at the crumbling old mansion for a funeral she wanders off to the secret garden. But when she reports the vision she had there, the family is engulfed in fear, violence, and madness. For Aunt Fanny's long-dead father has given her the precise date of the final cataclysm!