New Year 1924. Mary Russell is drawn into a new intrigue when she and her husband, Sherlock Holmes, pay a visit to Holmes' gravely ill brother, Mycroft. Mycroft has received a strange package that contains the papers of a missing English spy named Kimball O'Hara, the hero of Rudyard Kipling's Kim, who is feared to have been taken hostage - or even killed. Mary and Sherlock embark on a search for the missing operative, which takes them on a perilous journey through sun-drenched India. But when a twist of fate forces the couple to part ways, Russell learns that in this faraway place it's often impossible to tell friend from foe, and that some games must be played out until their deadly end.