Beautiful, young Irne St. Claire enlists Holmes' and Watson's help for her father, a former veteran of the Great Indian Mutiny, who has become a hopeless opium addict. His drug dependence is a direct result of guilt and fear arising from a blood pact of secrecy made during the siege of Agra in 1857 in which he was party to the theft of a maharajah's treasure, murder, and betrayal. When an avaricious co-conspirator dies under mysterious circumstances, St. Clair is certain that the curse will strike him next.