After the final defeat of the Ottoman Empire at the great naval battle of Lepanto, it seems that Europe is safe. But one day Nicholas Ingoldsby is summoned to London for an audience with the Queen herself. He is to go on a diplomatic mission to Constantinople, the heart of the old enemy - and then onward, to a little-known but rising power called Muscovy. Here the Russian Czar has just proposed marriage to Elizabeth herself. Such a bold offer should be no surprise, for this is no normal leader: Ivan IV Vasil'evich is known to his people as Ivan the Terrible. But this rising new Christian power in the North has also caught the attention of the Ottomans; and their allies, the wild Tatar horsemen of the Asiatic steppes, Russia's ancient enemy. And soon Nicholas and his fellow travellers, Smith, Stanley and the faithful Hodge, are caught up in their most dangerous adventure yet, trapped in a doomed Muscovy ruled by a deranged but cunning Czar Ivan, and with a vast army of Tatar tribesmen riding down upon them, vowed to burn the city to the ground and extinguish Russia forever...