The story of "the natural history of the most extraordinary creature that never existed". It posits the theoretical evolution of dragons from the Cretaceous period up to the 15th century, and theories about what dragon life and behaviour might have been like if they had existed and evolved. It uses the premise that the ubiquity of dragons in world mythology suggests that dragons could have existed. They are a species that are scientifically feasible and could have evolved, although they did not. The dragons featured in the show were designed by John Sibbick. The program switches between two stories. The first uses CGI to show the dragons in their natural habitat throughout history. The second shows the story of a modern day scientist at a museum, Dr. Tanner, who believes in dragons. When the frozen remains of an unknown creature are discovered in the Carpathian mountains, Tanner, and two colleagues from the museum, undertake the task to examine the specimen to try to save his reputation. Once there, they discover that the creature is a dragon. Tanner and his colleagues set about working out how it lived and died.