A good followup to the author's first novel in the series "The Strangler Vine". It follows the same formula - the impeccable historical research to spin a story out of relatively little-known events/characters, the Odd Couple protagonists that come together to solve a mystery gruesome enough to nudge the book into the Noir genre, Avery with the naive and biased views of the class of people he cannot identify with but growing to understand it, and Blake the worldly curmudgeon, etc. Even the predisposition of Avery to fall into effeminate protests when at odds with Blake rather than be a manly dude arguing with another is preserved from the first novel (perhaps unintentionally).
While the first book was set in India around the Thuggees, this novel returns to a much more familiar (to avid readers) setting of Victorian London whose misery and mystery are well documented in novels from Dickens to Doyle. But, it is the deep research into the underworld struggles and radical movements amidst the social unrest of the time prompted by the growing inequalities due to industrialization and directed against the "establishment" for the context, that sets it apart.
With some parallels to the growing social unrest of the current era prompted by the inequalities due to globalization, it is a small reminder of why history and historical accounts (even if fictionalized) are important enough to be read by all.