A 14-year-old maths genius plus a murdered maths tutor equals a complicated crime that has Homicide reaching for the textbooks. Mysterious equations scrawled across the victim's body pose a question that only the killer can answer. Maths whiz Liam Neades is sheltered from a normal childhood, but does that make him a killer? When his estranged older sister turns out to have a unique connection to the victim, suspicion falls on the family. Until a second murder presents the team with a whole new problem to solve. With Liam's upbringing touching a nerve, Allie struggles to stay objective. As her anger towards the family increases, so does Waverley's frustration with the detective's choices.