When a new ballet teacher arrives at Rookwood School, Scarlet and Ivy find themselves ensnared in a web of malice and unexplained accidents. The twins must navigate the rigid social hierarchy of their boarding school while investigating the sudden disappearance of their former instructor. Opposed by a mysterious new faculty member and a series of threatening letters, the sisters rely on their bond to uncover the truth. The narrative unfolds through a third-person perspective that emphasizes the atmospheric tension of the school setting and the girls' growing suspicion of the adults in charge.

This installment in the series maintains the established tone of school-based mystery that characterizes the previous entries. The narrative relies on the contrast between the seemingly improved conditions at Rookwood and the underlying threats that emerge with the arrival of new staff. Readers often note the effectiveness of the boarding school atmosphere in heightening the sense of vulnerability for the protagonists. The plot structure prioritizes the gradual accumulation of clues, ensuring that the mystery remains the primary focus throughout the school term.