"Suspended in the heavens is a net, made entirely of threads of light. The net hangs high above the palace of Indra, who in the east, is king of the gods. At every crossing of Indra′s net is a crystal gem, and each is illuminated, not only by its own light, but by the light of every other gem it reflects, and reflections of reflections, embracing an infinite galaxy. I am one such crystal; I am one, but reflect all. I am oft mistaken for the planet Venus, for in the night sky I am the most brilliant of stars. To the Romans I was Amante de Dio; the love of god. In India I am Varga, a name I share with thunderbolt, for we are as powerful as each other. In English, I am Diamond. If you were to examine Indra′s net more closely, you would think that its vertical threads run through space, and its horizontal threads through time. The measuring of time is a peculiarly human device, with little to recommend it, so let us for simplicity say that I am situated at the intersection of two threads; I connect two times and places, I am their meeting point; their narrator...."

Amen Corner, London, 1864. Orphan Sarah O'Reilly has disguised herself as a boy so that 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 on 'exceptional women' for the paper, and who takes Sarah under her wing.

Lily has been enlisted by Lady Cynthia Herbert to help catalogue her magnificent collection of jewels. She is especially struck by several large gems belonging to the Maharaja of Benares, which Lady Herbert has promised to have made into a special charm called a navaratna. The gems include a fiery red diamond that seems to exert 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 of whom have been strangled in a distinctive way. A local simpleton, Holy Joe, is blamed for the murders but neither Lily or Sarah are convinced the police have the right man. The trail of the missing gems leads them back to India and the dangerous cult of the destroyer goddess Kali.