In the summer of 1897, as royalty and notables from all over the world gather in London for Queen Victoria's Diamond Jubilee, a Canadian woman seeks help from Holmes to deal with the strangers who are following her about during her visit to Britain.

Investigations by Holmes reveals a connection with a society lady, a former beauty, whose fiance was murdered in Paris twenty years before, the death remaining unsolved. Gradually he unveils a story of a long-held vow of revenge, an act of unspeakable cruelty in the Tzar's Russia and the complications of revolutionary efforts, while he strives to protect his client from the denizens of the Tzar's intelligence service'.