One of the hottest summers on record is creating an adrenalin rush among Britain's aerial archaeologists. As their drones take to the skies, they are uncovering significant new finds emerging from the parched landscape. All over the country, hundreds of unknown historic sites have been revealed from the air. And it's not just the professionals that are striking gold - an army of drone-flying amateurs have made some incredible discoveries. In this Heatwave special edition of Hidden Britain by Drone, history and archaeology enthusiast Sir Tony Robinson investigates how this summer's long dry spell created the perfect conditions for the mysterious 'parch marks' that led to these remarkable discoveries. He meets the archaeologists and drone pilots that have been flying all over the country to record this transient phenomenon. Once it rains, the marks disappear, but the hidden secrets have been revealed - now it's a question of what happens next to these hidden historic gems.