A fossilised creature, millions of years old. is discovered by four young boys at the entrance to a cave. Their curiosity and imagination stimulated they decide to sail their boat down the river flowing from the cave. Down through the ages sails their little boat in search of the strange creature's place of evolution. Back to the canvas of primitive man; through treacherous landscapes with ferocious beasts and gigantic birds; on through the Mesozoic Era, the Palaeozoic Age of the amphibians, on foot through the Carboniferous Jungle and finally to the barren rocks overhanging the Silurian sea.

Journey into the Primeval Age is a children's film, intentionally based on Verne's conception of blending a fantastic story with scientific reality. Karel Zeman uses a variety of tricks and remarkably ingenious puppets in such a way that tire entire animal kingdom seems lifelike. Zeman had previously been noted for his puppet film Mr. Prokouk and the experimental Inspiration. In this film he seems to be following in the illustrious footsteps of the great magician, Georges Melies.