The Door in the Fog - A Foxglove Corners Mystery, #16

Jennet follows a wounded collie, until it appears to vanish in the fog-or through a blue door on a barn that subsequently vanishes as well. To add to the strangeness, Jennet's Christmas present from her sister, a nostalgic portrait of a girl with a collie litter, appears to come with a curse attached, one that bodes ill for the painting's owner.