The Aldens are helping one of Grandfather's friends break a world record by building the world's largest yo-yo! As they help with the project, strange things begin to happen. First someone follows them, and then the plans for the yo-yo turn up missing. Someone is trying to sabotage the yo-yo before it's launched! It seems there are a few people in Greenfield who don't want this yo-yo completed. The Boxcar Children will piece the evidence together to get to the bottom of this mystery. Someone tries to sabotage the world's largest yo-yo! Gertrude Chandler Warner grew up in Putnam, Connecticut. She wrote The Boxcar Children because she had always dreamed about what it would be like to live in a caboose or a freight car―just as the Aldens do. When readers asked for more adventures, Warner wrote more books―a total of nineteen in all. After her death, other authors have continued to write stories about Henry, Jessie, Violet, and Benny Alden, and today The Boxcar Children® series has more than one hundred books. Used Book in Good Condition