The Serpent of Rock Lake is book #2 in The Library Kids series and continues the adventure of Katie O'Conner and her friends after they find a secret library inside the Blue Mounds. Now they're on a mission to collect twelve crystals in order to stop the Dark Master and the Enemies of the Library, once and for all. But finding the first crystal won't be easy. The Library Kids adventure continues as the group takes a trip back in time to a Wisconsin homestead, which results in meeting Richard's maternal Ho-Chunk ancestors and a mysterious 15,000 year-old leprechaun. A meeting with Mother Earth and her eagle helper leads to a journey around the world and a way to save a precious piece of land next to the Library. Eventually, the group must face the serpent of Rock Lake to retrieve the first crystal.