A naked man's body is found in the middle of a strange crop circle at a farm owned by Sir Harry Chatwyn (John Woodvine), setting off an explosion of speculation as to how it got there. Most people believe it's the act of a supernatural being, a theory supported by alien expert Lloyd Kirby (Kenneth Colley). Detectives Tom Barnaby (John Nettles) and Gavin Troy (Daniel Casey) step in when another dead body is found.