In "Schoolhouse Mystery" by Gertrude Chandler Warner, a peculiar incident unfolds when an unusual man visits and exchanges ten dollars for an old quarter from Mr. Moss. This curious transaction intrigues the characters and raises questions about the man's intentions and the significance of the quarter. The encounter sets off a chain of events that pushes the young protagonists to investigate the mystery surrounding the man and the coin.
As they delve deeper into the situation, the children uncover hidden secrets and learn valuable lessons about curiosity and community. The strange man's visit not only adds an air of mystery to the story but also highlights themes of discovery and adventure as the characters navigate their small town's intriguing elements.