The TARDIS lands in Central Asia in 1289, with the Doctor and his companions joining the travelling caravan of Marco Polo, the Venetian explorer.  Travelling from the Pamir Plateau, through the Gobi Desert and into Imperial Cathay, they encounter many dangers, before meeting the aged Kublai Khan in Shang-Tu.  Travelling to Peking, the TARDIS team save Khan from an assassination team before travelling off in the TARDIS.