Conjure Wife by Fritz Leiber

The small restless breezes of night stirred the leaves of the venerable oak standing like some burly guardian beside the narrow house of the Carrs. Through the overlapping shadows softly gleamed the white of the walls -- such a spotless, pristine white that neighbors laughingly vowed the old lady herself came out after everyone had gone to sleep and washed them down with a long-handled mop. Everywhere was the impression of neatly tended, wholesome age. It even had an odor -- like some old chest which a clipper captain had used to bring back elegant spices from his voyages in the China Trade.

The house faced the campus. The girls could see it, going to classes, and it reminded them of afternoons they had spent there, sitting in straight-backed chairs, all on their best behavior, while a wood fire burned merrily on the shining brass andirons in the white fireplace. Mrs. Carr was such a strait-laced innocent old dear! But her innocence was all to the good -- it was no trouble at all to pull the wool over her eyes. And she did tell the quaintest stories with the most screamingly funny, completely unconscious points. And she did serve the nicest gingerbread with her cinnamon tea.