Archaeologists conduct a dig at Auckland Castle in Co Durham, which 700 years ago was home to a group of power-crazed bishops who behaved more like warriors than religious leaders. The experts head to Dirleton Castle in East Lothian to reveal the role one of the men played in defending England from William Wallace's army, and also try their hands at the art of stained glass-making, and fire a working trebuchet - the ultimate medieval weapon of war