The TARDIS materialises at the Roof of the World, Central Asia, in 1289. There they meet Marco Polo and his fellow travellers on their mammoth journey across the Pamir Plateau and through the Gobi desert to Peking. Unfortunately for the Doctor, his Ship proves to be of immense interest to Polo, who sets his mind on presenting it to the mighty Kublai Khan on arrival at his court.

But Polo isn't the only one with designs on the TARDIS. The war-like Tegana will go to any lengths to steal the magical blue box, lengths which endanger the lives of all the travellers. When the Doctor meets Kublai Khan himself, his precious Ship is his only collateral in a high-stakes game of backgammon, and Khan is a master of the game....

William Russell, Jacqueline Hill, and Carole Ann Ford co-star as the Doctor's companions, whilst Mark Eden plays the explorer Marco Polo. This story is currently missing from the BBC Television Archives.