The execution of a Vatican archivist within the shadow of the Kremlin exposes a conspiracy going back three centuries—to the bloody era of the Russian Tsars. Before his murder, he manages to dispatch a coded message, a warning of a terrifying threat, one tied to a secret buried within the Golden Library of Tsars, a vast and treasured archive that had vanished into history.

As combative forces race for the truth behind this death and alarming discovery, Sigma Force is summoned to aid in the search—not only for this missing trove of ancient books, but to follow a trail far into...