Task with one diamond

Journalist Julia Smirnova accidentally learns about the hunt for an old diamond with an incredible story. At first, the British took him out of India, then he ended up in Russia to save one of the daughters of Nicholas II. The English descendants of the adventurer who visited Russia in 1918 were involved in the case, and the Millers" family, from whom he bought a daughter for this diamond for exchange for the Grand Duchess. Participants in those events are long dead, but the stone behind which the bloody trail stretches requires more and more victims. How to stop the murders? Where is the diamond now? Why are the descendants of the participants in the events of a hundred years ago right now gathered in St. Petersburg?