Missing episodeArriving in Central Asia in 1289, the Doctor and his companions join the caravan of the famous Venetian explorer Marco Polo as it makes its way from the snowy heights of the Pamir Plateau, across the treacherous Gobi Desert and through the heart of imperial Cathay.Having witnessed many incredible sights and survived a variety of dangers, they arrive at the mighty Kublai Khan's Summer Palace in Shang-tu, where the Doctor strikes up an extraordinary friendship with the now-aged ruler.They move on at last to the even more sumptuous Imperial Palace in Peking, where the travellers save the Khan from an assassination attempt by the Mongol warlord Tegana — supposedly on a peace mission — before departing once more in the TARDIS.