Bicycle 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 on a bicycle trip.

On the first night of their journey, the Boxcar Children get caught in a rainstorm. They find shelter in an old abandoned house -- and a mystery finds them!