Cam, her best friend Eric, and Eric's mom are spending the day with Eric's grandparents. But Grandpa and Grandma seem too tired to visit. Every so often, a knock at the door wakes them up. But when they go to answer, no one is there. Is a Knock, Knock Ghost on the loose? It's up to Cam to solve the mystery! Garden State Children's Book Award 2017 Nominee.
"The stories in the this series promote logical thinking and helpfulness for young readers beginning to enjoy simple transitional chapter books." (School Library Journal)