"The mark of the monster by Jack Williamson" is a pulp horror short story written in the early 20th century. Set in a decaying Appalachian town steeped in occult lore, it follows a young man’s return to a place of brooding superstition, where whispered talk of a monstrous twin, a blood-smeared cellar, and a hilltop altar entwine love, fear, and the suggestion of inhuman inheritance. Claiborne Coe comes back to Creston to marry Valyne, despite a dire warning from his foster father, Doctor Kyle. After a brutish encounter with Jud Geer and glimpses of a chained “creature” in the cellar, Kyle convinces Clay he is half-demon with a monstrous twin. When the “monster” escapes and abducts Valyne to the forest altar, Clay fights it; Kyle’s rifle shot fells the beast. Valyne then reveals the ticking of Jud’s watch, exposing the “monster” as Jud in a mask. Kyle confesses a plot—abetted by his household—to terrorize Clay into suicide and seize his fortune, and when he turns his gun on them, Clay kills him in self-defense. Clay and Valyne leave Creston for good. (This is an automatically generated summary.)