Fall has come upon Wolfhollow, New Hampshire where the days are shorter and the nights cooler. Leah, Avery, and Grayson Bartlett have started back into the rhythm of their school year. However, a family friend asks the children to help him with a research project for an ancestor who traveled the historical Underground Railroad, with a stop near the Bartlett home in Wolfhollow, New Hampshire. What starts off as field trips to local museums turns into an adventure filled with an underground train, a snake pit, and a rope bridge over waterfalls. Along the way the Rucksack Kids help solve a decades-old crime. The local newspaper nicknamed the Bartlett children the 'Rucksack Kids' for the canvas backpacks they each carry. The rucksack contents, like the Bartlett children's different personalities, contain a variety of tools and gadgets that they use to help solve mysteries.