1Cynghanedd
Looking for a middle-grade book I read around 2010. It was a short, breezy chapter book targeted for the elementary/middle grade range, could have been a Scholastic book. I believe the story involved a group a kids trying to solve a mystery at their school. There might have been infrequent cartoony illustrations, maybe one per chapter. The main detail I remember is that one of the characters was described as liking prune juice (at least I think it was prune juice) and being able to walk, talk, and write simultaneously. I believe he wore glasses and was named Quincy. If anyone is good at text queries, hopefully "prune juice" or "walk, talk, and write at the same time" might ping something?

