When a series of suspicious deaths strikes a charismatic religious movement, Mary Russell must navigate the intersection of theology and crime to uncover a lethal conspiracy. As a newly independent Oxford graduate, Russell seeks to balance her burgeoning intellectual partnership with Sherlock Holmes against her own growing fascination with the New Temple of God. The narrative, presented through Russell's sharp, first-person perspective, forces her to confront the charismatic leader Margery Childe while managing the evolving, complex emotional dynamic she shares with the retired detective. As the stakes rise with the deaths of wealthy women, Russell and Holmes must apply their distinct analytical methods to a world shifting under the influence of post-war social change.

This novel is widely regarded for its successful expansion of the Sherlock Holmes mythos by introducing a protagonist who challenges the traditional detective archetype. Readers and critics frequently highlight the balance between the historical detail of the 1920s and the evolving psychological depth of the relationship between Russell and Holmes. The work is noted for its integration of theological inquiry into the structure of a classic mystery, providing a distinct tone that separates it from standard pastiches. The narrative pacing is often praised for its steady build, allowing the philosophical questions raised by the New Temple of God to carry as much weight as the central criminal investigation.