The TARDIS crew lands in the Himalayas of Cathay in 1289, their ship badly damaged, and are picked up by Marco Polo's caravan on its way along the fabled Silk Road to see the Emperor Kublai Khan. The story concerns the Doctor and his companions' attempts to thwart the machinations of Tegana, who attempts to sabotage the caravan along its travels through the Pamir Plateau and across the treacherous Gobi Desert, and ultimately to assassinate Kublai Khan in Peking, at the height of his imperial power..