The Yellow House 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 determined to solve the mystery that surrounds an old yellow house on his property. Strange things have happened in that house where long ago a man disappeared.

When the Boxcar Children explore the house, they find an old letter written by the brother of the man who vanished! And that's only the first startling discovery they make when they set out to investigate The Yellow House Mystery.