A flurry of unexplained suicides has recently occurred among the wealthy elite of London high society. Intrepid sleuth Sherlock Holmes believes the perpetrator is cunning seductress Adrea Spedding, a woman who perpetually haunts London's gambling halls in search of her unlucky prey. Now Holmes, with help from his steadfast assistant, Dr. Watson, must draw Spedding out by playing the role of her next victim.

When a gentlewoman is found dead with her throat torn out, the villagers blame a supernatural monster. But Sherlock Holmes, who gets drawn into the case from nearby Quebec, suspects a human murderer.

Holmes and Watson travel to Washington D.C. in order to prevent a secret document from falling into enemy hands.