In the fall of 1934, Tillie Tilden travels to Rosemount, Minnesota, to teach kindergarten through eighth grade in a one-room schoolhouse. The community is thrilled that she accepted the position on such short notice, and Tillie is excited about taking a break from classwork and getting some real-world experience. She loves her students, particularly a sweet, mentally challenged sixth grader named Orville. But as she settles into her new role, she grows concerned. Why is nobody willing to tell her what happened to the previous teacher? Eventually, Tillie learns that Helen Shattuck was found hanging from the rafters of the school's storage room. The townsfolk assume she ended her life because of an unwanted pregnancy. But when Tillie discovers her diary hidden in the place where she died, she suspects that the teacher was murdered -- possibly by someone high up in the school district. Now Tillie is determined to bring the killer to justice. To succeed, she'll need the help of Al Freitag, the handsome sheriff's deputy, and Orville, the student she's never given up on.