Outdoor Girls at Wild Rose Lodge, The by Laura Lee Hope

In this 11th book in the "Outdoor Girls" series, the girls have some very exciting experiences. An old man, Professor Dempsey, by name, who had retired to a little log cabin in the woods to recover his health, had chanced to do the girls a very great favor. Of course the girls were grateful to him and were very much interested when he told them of his two sons who were in the war. Later, when the girls read of the death of his two sons in the paper, they went to the old man's lonely cabin in the woods, but found themselves too late. According to a friendly neighbor, the old man had become temporarily insane at the terrible news, had wrecked his cabin in an insane frenzy, and disappeared.

Later, at Wild Rose Lodge, the girls were frightened several times by a strange apparition lurking in the woods around the lodge and Moonlight Falls, a beautiful fall of water not far from the cottage where the girls were staying. The boys came home from France and helped the girls solve the mystery. (Summary from the next book)

Laura Lee Hope is a pseudonym used by the Stratemeyer Syndicate for several series of children's and young adult novels.