Barney is a solitary little boy, given to wandering off by himself. One day he is lying on the edge of a disused chalk-pit when it gives way and he lands in a sort of cave. Here he meets a boy wearing a rabbit skin and speaking in grunts. He names him Stig. Nobody believes Barney when he tells his family all about Stig, but they become great friends, learning each others ways and embarking on a series of unforgettable adventure