Rosie Franklin loves a good mystery but never expected one to hit so close to home. The day after Brown Intermediate's annual field day festival, three of Rosie's classmates are out sick. The next day, three more students are missing from class, and then another the following day. While the rumors fly, nobody knows what is making the students sick. Luckily for Rosie, her Aunt Liv is an epidemiologist-a disease detective. Rosie learns that unraveling the mystery gets more difficult as time passes and the stakes grow higher. It is up to Rosie to grab her best detective fedora, lean into her curiosity superpower, and join forces with friends (and an arch-nemesis) to reveal the illness' true identity. We follow Rosie to school, a disastrous softball game, and even a public health laboratory as she learns more about both epidemiology and herself on her first adventure as a disease detective.