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 in a lighthouse. But strange things begin to happen around the lighthouse, and soon the Boxcar Children embark on another delightful adventure.

The Aldens take a trip to the New England coast and get to stay in a lighthouse But strange things happen after it gets dark--an unknown woman is seen walking around, and Watch wakes up growling late at night. Can the Boxcar Children shed light on a seaside mystery?