Theo Chalmers interviews crop circle researcher and author Andy Thomas about those enigmas of grain; those carbohydrate conundra; those puzzles in the fields; those mystifying and transient ephemera. Looking at their history, how they are evolving, their diversity, their biology, whether some or all of them are made by mad cereal killers with a stake, a rope and a board, and if not, what the circles are trying to tell us.