Twelve-year-old Myrtle Hardcastle has a passion for justice and an obsession with criminal science. Armed with her father’s law books and her mum’s microscope, Myrtle studies toxicology, keeps abreast of the latest developments in crime scene analysis, and observes her neighbors in the quiet village of Swinburne, England. When her neighbor dies under Mysterious Circumstances, Myrtle seizes her chance. With her unflappable governess, Miss Ada Judson, by her side, Myrtle takes it upon herself to prove Miss Wodehouse was murdered and find the killer, even if nobody else believes her — not even her father, the town prosecutor.