1571. At the great naval battle of Lepanto the Ottoman Empire is finally defeated, and it seems that Europe is safe. But then Nicholas Ingoldsby is summoned to London by the Queen herself and sent on a diplomatic mission to Constantinople, the heart of the old enemy - and then onward, to a little-known but rising power called Muscovy, ruled by a deranged but cunning czar - Ivan the Terrible. The rise of Muscovy has also caught the attention of the Ottomans; and their allies, the wild Tatar horsemen of the Asiatic steppes, Russia's ancient enemy. Soon Nicholas and his fellow travellers are caught up in their most dangerous adventure yet, trapped in a doomed Muscovy with a vast army of Tatar tribesmen riding down upon them, vowed to burn the city to the ground and extinguish Russia for ever...