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 helping their neighbors build a tree house. From the new tree house, the Aldens can keep an eye on the house next door. That house has a very old and special secret...and the Boxcar Children are determined to find out what it is!