Fog Magic by Julia L. Sauer (Ex-Library Paperback)

A Newbery Honor Book. Greta had always loved the fog—the soft gray mist that rolled in from the sea and drifted over the village. The fog seemed to have a secret to tell her. Then one day when Greta was walking in the woods and the mist was closing in, she saw the dark outline of a stone house against the spruce trees—a house where only an old cellar hole should have been. Then she saw a surrey come by, carrying a lady dressed in plum-colored silk. The woman beckoned for Greta to join her, and soon Greta found herself launched on an adventure that would take her back to a past that existed only through the magic of the fog.