Amen Corner, London, 1864. Orphan Sarah O'Reilly disguises herself as a boy so she can work in the offices of Septimus Harding's newspaper, the London Mercury. There she meets Lily Korechnya, a wealthy widow who writes a column under a pseudonym, and takes Sarah under her wing.
Lily is enlisted by Lady Cynthia Herbert to catalogue her magnificent jewel collection. She is intrigued by several gems belonging to the Maharaja of Benares, including a fiery red diamond which exerts an unsettling influence over anyone who touches it.
Then two gruesome murders take place — first a customs officer at the docks and then a jeweller in Hatton Gardens, both strangled. A local simpleton, Holy Joe, is accused of murder but neither Lily or Sarah are convinced the police have the right man. The trail of the missing gems leads them back to India, to ghosts, and the dangerous cult of the destroyer goddess Kali.
