The Secret of the Sundial by Mildred A. Wirt

On a certain evening in early September—Friday the thirteenth—to be exact, a stranger in Claymore, Michigan, might have been startled to behold two figures, grotesque in long white sheets which draped them from head to foot, scurrying along an alley leading to Summit Street. It was an appropriate night for ghosts to be abroad. The moon was in the dark and the wind whistled weirdly through the trees.