A few weeks after Mystery in Malakand ends, Hester’s life is back to normal in Peshawar, and she is finding this difficult and dull. Her relationship with Sir John remains unresolved – and she cannot work out what his intentions are. When she is contacted by the Delhi Intelligence Bureau and invited to Delhi to discuss a project, she is intrigued. She travels down to the heart of the Empire and is received at DIB Headquarters where they ask for her help in spying on the Russians in Chinese Turkestan. She jumps at the chance.
Her mission is to make contact with and befriend a White Russian, Captain Vilgoski, in Chinese Turkstan. Vilgoski is giving the British intelligence on Bolshevik intentions in China, but DIB has reason to believe they cannot trust him. They need Hester to get close enough to him to find out the truth. First, however, she undergoes a crash course in some of the techniques of espionage. When her training is complete she is sent across the Karakorum Mountains to Kashgar to be briefed further by the British Consul.
Her cover is as a nurse accompanying a British archaeological expedition travelling in a caravan beyond the Yarkand River, across the forbidding Taklamakan Desert along the path of the ancient Sillk Route. Their destination is the Flaming Mountains in Xinjiang province. She communicates her information back to Peshawar disguised in regular reports to the hospital. Sir John, the Chief Commissioner acts as the intermediary with the DIB and therefore becomes intricately involved in her expedition.
Hester meets a group of characters who all have secrets to hide. This includes the chief British archaelogist, Dr William Arnold, the Cossack General Ataman Dutov, and the pro-Bolshevik Amban of Yarkand. When the Cossack General is murdered suspicion falls immediately on Hester’s White Russian friend, Vilgoski. But she is beginning to think he might be innocent and sets out to prove it by finding the real murderer. Sir John, who is far away, is galled by the fact that that she has formed an alliance with Vilgoski but decides that he must do what he can to help. He and Hester work together to unpick the complex intrigues and find the killer.