The Animal Shelter 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 that they have a home with their grandfather, they've turned their old boxcar into a home for stray animals!

When the Greenfield Animal Shelter is forced to close, the Boxcar Children offer to care for the abandoned animals. But then they discover that many belong to an old woman who appears to be missing. Where is she? And who are the strange men living in her house? Before they know it, the children have another mystery to solve.