The first stone henge to be discovered in Britain for a century would be cause enough for major celebration. But there's double bubbles as Tony Robinson and his hardy team of archaeologists celebrate their 200th dig. The site is the bed of a Devon reservoir with a strange assortment of prehistoric remains. The reservoir has been specially drained, but the diggers still face three days of wading through thick, sticky mud as they piece together the story of thousands of years of rituals performed in this beautiful secret valley high up on Dartmoor. The Team slowly uncover a network of monuments that suggest they have found a major prehistoric site. But the best discovery is left until the last day when they unearth the remains of that stone henge. It's the perfect end to a milestone in the programme's history