Queen Marie of Roumania, granddaughter to both Victoria, Empress of the British Empire, and Alexander II, Tsar of Russia, is in need of Mary Russell and Sherlock Holmes' services. The Queen, a famous beauty who has transformed Roumania from a quiet backwater into a significant force, invites the pair to Bran castle, the ancient fortress that sits on the border with the newly regained territory of Transylvania.

The threat the Queen fears is dubious: shadowy figures, vague whispers, dangers that may only be accidents. But a young girl is involved. So, putting aside their doubts, Russell and Holmes set out to investigate the mystery in a land of long memory and hidden corners, from whose churchyards the shades creep.