Thirteenth-century China, and the legendary Kublai Khan rules over Cathay and the Middle Kingdom. Of his many ministers and advisors, his favourite is a foreigner - the Venetian Marco Polo, whose understanding of the language and etiquette of the court is exemplary, and whose advice is widely sought. So when a flood of portents, strange visions and ghastly murders occur throughout the kingdom and even across the oceans, Marco's wisdom is called upon. The leaders of a demonic sect have disappeared from the desert to which they were banished, and Kublai Khan believes that they will attempt to release the Plague Lord himself, and open the gates of Hell...