The Secret at Lone Tree Cottage
It’s a Dana Girls mystery! Louise (dark hair) and Jean (the blond) are the Dana sisters, still in high school, yet capable of solving intriguing mysteries devised by Mildred Wirt Benson (pen name- Carolyn Keene) the author who is still alive evidently; last year turning 105 yrs. old! I love this author; the one with the daring plots and real life pilot experience, but she didn’t write this particular one in the series according to Wikkipedia; keep in mine they are not always accurate in their information, but this does sound believable as I recall from reading a book about Mildred Benson a few years ago.
Leslie McFarlane is the author to the first 4 of the Dana Girls (says Wikipedia) Leslie is a man- photo below.
Mildred Benson author below
This particular mystery is about the girl’s beloved English teacher Miss Tinsdel’s disappearance. She was last seen leaving Stardurst school where Jean and Louise attend. Who took her? Why? She has a sister . Uncle Ned helps on this case.