1869. Tibet is closed to Europeans, an infuriating obstruction for the rap­idly expanding British Empire. In response, Britain begins training Indians-permitted to cross borders that white men may not-to undertake illicit, dangerous surveying expeditions into Tibet.

Balram is one such surveyor-spy, an Indian schoolteacher who, for several years, has worked for the British, often alongside his dearest friend, Gyan. But Gyan went missing on his last expedition and is rumored to be imprisoned within Tibet. Desperate to rescue his friend, Balram agrees to guide an English captain on a foolhardy mission: After years of paying others to do the exploring, the captain, disguised as a monk, wants to personally chart a river that runs through southern Tibet. Their path will cross fatefully with that of another Westerner in disguise, fifty-year-old Katherine. Denied a fellowship in the all-male Royal Geographical Society in London, she inten