In the early days of 1924 Mary Russell and her husband, the inimitable Sherlock Holmes, are given an urgent task by his brother Mycroft: Find a British spy gone missing along India's northwest frontier, where men are dying and trouble is brewing.

The spy's name? It is one Holmes knows from his sojourn in India long ago, and one Russell knows from a book. It is Kimball O'Hara, known to the world by the name Rudyard Kipling called him - Kim...