When Neale and Margie Lawson hear that their father will have to sell his shore land and their beloved horse, Firefly, they are miserable. They can find no way to help until a strange red car, a lost cat, and the odd behavior of an eccentric old man draw them into a mystery involving the lost letters of a famous New England artist. The Lawsons and their friend Rupert Reed, son of the Ranger at the camp across the lake, are plunged into a bewildering tangle of strange doings. Neale thinks that his robot-burglar alarm might help to solve the mystery, and Margie is sure that her grandfather's books hold the key to the problem. Both children are right, but it takes two discoveries - one in a cave on the mountain and one in the middle of Shadow Pond - to set things straight. Mary Jane's earlier mysteries, all exciting and fun to read, have found an appreciative audience. "Mystery at Shadow Pond" will add new friends to the large number of boys and girls who look forward to a book by this favorite author.