When they take their dog, Watch, for obedience training, the Alden children discover that some of the dogs in the class have vanished and decide to try to solve the mystery of their disappearance.

While visiting a small town in Alabama, the Aldens hear mysterious howls at midnight, leading them to wonder if an old local legend about a ghost dog is true.

"Henry, Jessie, Violet, and Benny used to live in a boxcar. Now they have adventures everywhere they go. At a lighthouse, the children find a mystery in the night!"