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, they get caught in a rainstorm, and take shelter in a mysterious, abandoned farm house.

Henry, Jessie, Violet, and Benny used to live alone in a boxcar. Now they have a home with their grandfather, and are spending the summer mountain climbing in New England. A dangerous rockslide, a mountain cave, and a secret treasure are a few of the adventures in store for the boxcar children!