Mary Russell is drawn into a new intrigue at the start of the New Year, 1924, when she and her husband, Sherlock Holmes, pay a visit to Holmes' gravely ill brother, Mycroft. Mycroft received a strange package that contained the papers of a missing English spy named Kimball O'Hara, who is feared to have been taken hostage.or even killed. The duo 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...