My Little Pony: Ponyville Mysteries: Schoolhouse of Secrets by "Penumbra Quill" (collective pen name of Michael Vogel and Nicole Dubuc) is the twenty-fifth book in a series of chapter books published by Little, Brown and Company and the first entry in the "Ponyville Mysteries" series. In this book, the Cutie Mark Crusaders attempt to solve a strange mystery at the Ponyville Schoolhouse that appears to revolve around new student Lilymoon.