Doubled in Diamonds is a 1966 spy thriller novel by the British Victor Canning.Reilly p.254 It is the second in a series of four novels about Rex Carver, a private detective drawn back into his old profession of espionage.Murphy p.79Burton p.81
Synopsis Carver is hired to find a man who has failed to claim an inheritance, who is turns out has been involved in a diamond heist. His mission takes him to Dublin and France, and draws him into a plot overseen by two Chinese twins, who are agents of the communist government, to sell drugs and earn hard currency for their country.
References
Bibliography Burton, Alan. Historical Dictionary of British Spy Fiction. Rowman & Littlefield, 2016. Murphy, Bruce F. The Encyclopedia of Murder and Mystery. Springer, 1999. Reilly, John M. Twentieth Century Crime & Mystery Writers. Springer, 2015.