The Guide Dog Mystery — Gertrude Chandler Warner

One warm night four children stood in front of a bakery. No one knew them. No one knew where they had come from.

Henry, Jessie, Violet, and Benny used to live alone in a boxcar. Now they have a home with their grandfather, and are going to visit a guide dog school.

But once the Aldens arrive at the school, mysterious things start to happen. Benny sees strange lights in one of the dormitory rooms, and late one night, someone breaks into the kennel where the guide dogs are kept. Is someone after one of the dogs? The Boxcar Children are determined to find out!