It posits a speculative evolution of dragons from the Cretaceous period up to the 15th century, and suppositions about what dragon life and behavior 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 depicted as a scientifically feasible species of reptile that could have evolved, somewhat similar to the depiction of dragons in the "Dragonology" series of books. 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. The docufiction features two interwoven stories. Jack Tanner, an American paleontologist working for the Natural History Museum in London, suggests the theory that a carbonized Tyrannosaurus rex skeleton on display was killed by a dragon, causing him to believe that the legends were more than myth. This ruins Tanner's reputation. As viewed in a flashback, Tanner's theory is proven true, as said Tyrannosaurus battles a female dragon in the Cretaceous but is mortally wounded. The female dies from her wounds, forcing her infant to survive on his own, escaping a male dragon by learning how to fly for the first time. A later vignette shows the dragon, now an adult, trying to mate. The museum is contacted by Romanian authorities, who discovered an alleged corpse of a dragon in the Carpathian Mountains, along with two carbonized human bodies from the 15th century. Tanner and two colleagues are sent to examine the bodies, moved to a warehouse. The scientists are baffled by the corpse, discovering despite being , it was capable of both flight and breathing fire by storing bacteria and hydrogen inside its body. Marine dragons survived the KT extinction, before evolving into other subspecies, such as a Chinese forest dragon, able to glide on its smaller wings and capable of camouflaging itself. The forest dragon hunts a wild boar and Bengal tiger, but the arrival of humans in the forest challenges its survival. By analysing the dead dragon's reproductive system, Tanner concludes the corpse is that of an infant, killed by the humans.