Complex sentence: The Russian agent was well-informed about British India, but proved unscrupulous; believing he had succeeded, Younghusband did not reckon on Petrovsky's deal with the "Taotai", the Chinese governor of Hunza.
Split into simpler sentences: The Russian agent was well-informed about British India, but proved unscrupulous. Believing he had succeeded, Younghusband did not reckon on Petrovsky's deal with the "Taotai," the Chinese governor of Hunza.